Blood-clotting tests Health Dictionary

Blood-clotting Tests: From 1 Different Sources


Tests to screen for and diagnose bleeding disorders, usually resulting from deficiencies or abnormalities of blood coagulation factors or of platelets (see blood clotting). Tests are also used to monitor treatment with anticoagulant drugs.
Health Source: BMA Medical Dictionary
Author: The British Medical Association

Blood Pressure

Blood pressure is that pressure which must be applied to an artery in order to stop the pulse beyond the point of pressure. It may be roughly estimated by feeling the pulse at the wrist, or accurately measured using a SPHYGMOMANOMETER. It is dependent on the pumping force of the heart, together with the volume of blood, and on the elasticity of the blood vessels.

The blood pressure is biphasic, being greatest (systolic pressure) at each heartbeat and falling (diastolic pressure) between beats. The average systolic pressure is around 100 mm Hg in children and 120 mm Hg in young adults, generally rising with age as the arteries get thicker and harder. Diastolic pressure in a healthy young adult is about 80 mm Hg, and a rise in diastolic pressure is often a surer indicator of HYPERTENSION than is a rise in systolic pressure; the latter is more sensitive to changes of body position and emotional mood. Hypertension has various causes, the most important of which are kidney disease (see KIDNEYS, DISEASES OF), genetic predisposition and, to some extent, mental stress. Systolic pressure may well be over 200 mm Hg. Abnormal hypertension is often accompanied by arterial disease (see ARTERIES, DISEASES OF) with an increased risk of STROKE, heart attack and heart failure (see HEART, DISEASES OF). Various ANTIHYPERTENSIVE DRUGS are available; these should be carefully evaluated, considering the patient’s full clinical history, before use.

HYPOTENSION may result from super?cial vasodilation (for example, after a bath, in fevers or as a side-e?ect of medication, particularly that prescribed for high blood pressure) and occur in weakening diseases or heart failure. The blood pressure generally falls on standing, leading to temporary postural hypotension – a particular danger in elderly people.... blood pressure

Blood

Blood consists of cellular components suspended in plasma. It circulates through the blood vessels, carrying oxygen and nutrients to the organs and removing carbon dioxide and other waste products for excretion. In addition, it is the vehicle by which hormones and other humoral transmitters reach their sites of action.

Composition The cellular components are red cells or corpuscles (ERYTHROCYTES), white cells (LEUCOCYTES and lymphocytes – see LYMPHOCYTE), and platelets.

The red cells are biconcave discs with a diameter of 7.5µm. They contain haemoglobin

– an iron-containing porphyrin compound, which takes up oxygen in the lungs and releases it to the tissue.

The white cells are of various types, named according to their appearance. They can leave the circulation to wander through the tissues. They are involved in combating infection, wound healing, and rejection of foreign bodies. Pus consists of the bodies of dead white cells.

Platelets are the smallest cellular components and play an important role in blood clotting (see COAGULATION).

Erythrocytes are produced by the bone marrow in adults and have a life span of about 120 days. White cells are produced by the bone

marrow and lymphoid tissue. Plasma consists of water, ELECTROLYTES and plasma proteins; it comprises 48–58 per cent of blood volume. Plasma proteins are produced mainly by the liver and by certain types of white cells. Blood volume and electrolyte composition are closely regulated by complex mechanisms involving the KIDNEYS, ADRENAL GLANDS and HYPOTHALAMUS.... blood

Blood Clot

A blood clot arises when blood comes into contact with a foreign surface – for example, damaged blood vessels – or when tissue factors are released from damaged tissue. An initial plug of PLATELETS is converted to a de?nitive clot by the deposition of FIBRIN, which is formed by the clotting cascade and erythrocytes. (See COAGULATION.)... blood clot

Blood Count

The number of each of the cellular components per litre of blood. It may be calculated using a microscope or by an automated process.... blood count

Blood Transfusion

See TRANSFUSION – Transfusion of blood.... blood transfusion

Blood-poisoning

See SEPTICAEMIA.... blood-poisoning

Abo Blood Groups

See BLOOD GROUPS.... abo blood groups

Blood Bank

A department in which blood products are prepared, stored, and tested prior to transfusion into patients.... blood bank

Blood Brain Barrier

A functional, semi-permeable membrane separating the brain and cerebrospinal ?uid from the blood. It allows small and lipid-soluble molecules to pass freely but is impermeable to large or ionised molecules and cells.... blood brain barrier

Blood Corpuscle

See ERYTHROCYTES and LEUCOCYTES.... blood corpuscle

Blood Donor

An individual who donates his or her own blood for use in patients of compatible blood group who require transfusion.... blood donor

Blood Gases

Speci?cally, this describes the measurement of the tensions of oxygen and carbon dioxide in blood. However, it is commonly used to describe the analysis of a sample of heparinised arterial blood for measurement of oxygen, carbon dioxide, oxygen saturation, pH, bicarbonate, and base excess (the amount of acid required to return a unit volume of the blood to normal pH). These values are vital in monitoring the severity of illness in patients receiving intensive care or who have severe respiratory illness, as they provide a guide to the e?ectiveness of oxygen transport between the outside air and the body tissues. Thus they are both a guide to whether the patient is being optimally ventilated, and also a general guide to the severity of their illness.... blood gases

Blood Test

Removal of venous, capillary or arterial blood for haematological, microbiological or biochemical laboratory investigations.... blood test

Blood Vessel

Tube through which blood is conducted from or to the heart. Blood from the heart is conducted via arteries and arterioles through capillaries and back to the heart via venules and then veins. (See ARTERIES and VEINS.)... blood vessel

Blood Groups

People are divided into four main groups in respect of a certain reaction of the blood. This depends upon the capacity of the serum of one person’s blood to cause the red cells of another’s to stick together (agglutinate). The reaction depends on antigens (see ANTIGEN), known as agglutinogens, in the erythrocytes and on ANTIBODIES, known as agglutinins, in the serum. There are two of each, the agglutinogens being known as A and B. A person’s erythrocytes may have (1) no agglutinogens, (2) agglutinogen A, (3) agglutinogen B, (4) agglutinogens A and B: these are the four groups. Since the identi?cation of the ABO and Rhesus factors (see below), around 400 other antigens have been discovered, but they cause few problems over transfusions.

In blood transfusion, the person giving and the person receiving the blood must belong to the same blood group, or a dangerous reaction will take place from the agglutination that occurs when blood of a di?erent group is present. One exception is that group O Rhesus-negative blood can be used in an emergency for anybody.

Agglutinogens Agglutinins Frequency
in the in the in Great
Group erythrocytes plasma Britain
AB A and B None 2 per cent
A A Anti-B 46 per cent
B B Anti-A 8 per cent
O Neither Anti-A and 44 per cent
A nor B Anti-B

Rhesus factor In addition to the A and B agglutinogens (or antigens), there is another one known as the Rhesus (or Rh) factor – so named because there is a similar antigen in the red blood corpuscles of the Rhesus monkey. About 84 per cent of the population have this Rh factor in their blood and are therefore known as ‘Rh-positive’. The remaining 16 per cent who do not possess the factor are known as ‘Rh-negative’.

The practical importance of the Rh factor is that, unlike the A and B agglutinogens, there are no naturally occurring Rh antibodies. However, such antibodies may develop in a Rh-negative person if the Rh antigen is introduced into his or her circulation. This can occur (a) if a Rh-negative person is given a transfusion of Rh-positive blood, and (b) if a Rh-negative mother married to a Rh-positive husband becomes pregnant and the fetus is Rh-positive. If the latter happens, the mother develops Rh antibodies which can pass into the fetal circulation, where they react with the baby’s Rh antigen and cause HAEMOLYTIC DISEASE of the fetus and newborn. This means that, untreated, the child may be stillborn or become jaundiced shortly after birth.

As about one in six expectant mothers is Rh-negative, a blood-group examination is now considered an essential part of the antenatal examination of a pregnant woman. All such Rh-negative expectant mothers are now given a ‘Rhesus card’ showing that they belong to the rhesus-negative blood group. This card should always be carried with them. Rh-positive blood should never be transfused to a Rh-negative girl or woman.... blood groups

Clotting Time

See COAGULATION.... clotting time

Fetal Blood Sampling

A procedure performed during a mother’s labour in which a blood sample is taken from a vein in the scalp of the FETUS. This enables tests to be performed that indicate whether the fetus is, for example, suffering from a shortage of oxygen (HYPOXIA). If so, the obstetrician will usually accelerate the baby’s birth.... fetal blood sampling

Red Blood Cell

See ERYTHROCYTES; BLOOD.... red blood cell

Blood Root

Sanguinaria canadensis. N.O. Papaveraceae.

Habitat: Widely distributed throughout North America.

Features ? Root reddish-brown, wrinkled lengthwise, about half-inch thick. Fracture short. Section whitish, with many small, red resin cells which sometimes suffuse the whole. Heavy odour, bitter and harsh to the taste.

Part used ? Root.

Action: Stimulant, tonic, expectorant.

Pulmonary complaints and bronchitis. Should be administered in whooping-cough and croup until emesis occurs. The powdered root is used as a snuff in nasal catarrh, and externally in ringworm and other skin eruptions. The American Thomsonians use it in the treatment of adenoids. Dose, 10 to 20 grains of the powdered root.... blood root

Vision Tests

Most vision tests examine a person’s sharpness of VISION (visual acuity) and often of the ?eld of vision (see VISION, FIELD OF). Refraction tests assess whether a person has an error that can be corrected with glasses such as ASTIGMATISM, HYPERMETROPIA or MYOPIA. Visual acuity is tested using a Snellen chart when the patient tries to read letters of di?ering standard sizes from 6 metres away. The optician will prescribe lenses to correct any defects detected by vision tests.... vision tests

White Blood Cell

See LEUCOCYTES.... white blood cell

Pregnancy Tests

There are several tests for pregnancy (see PREGNANCY AND LABOUR) in its early stages, and these can be done on blood or urine; some of the urine tests may be carried out at home. Most tests are based on the detection of HUMAN CHORIONIC GONADOTROPHIN (HCG) in the woman’s urine. They are nearly 100 per cent accurate and may show positive as early as 30 days after the ?rst day of the last normal period.

The haemagglutination inhibition test This, and the subsequent tests to be mentioned, are known as immunological tests. They are based upon the e?ect of the urine from a pregnant woman upon the interaction of red blood cells, which have been sensitised to human gonadotrophin, and anti-gonadotrophin serum. They have the great practical advantage of being performed in a test-tube or even on a slide. Because of their ease and speed of performance, a result can be obtained in two hours.

Enzyme-linked immunosorbent assay (ELISA) This is the basis of many of the pregnancy-testing kits obtainable from pharmacies. It is a highly sensitive antibody test and can detect very low concentrations of human chorionic gonadotrophin. Positive results show up as early as ten days after fertilisation – namely, four days before the ?rst missed period.

Ultrasound The fetal sac can be detected by ULTRASOUND from ?ve weeks, and a fetal echo at around six or seven weeks (see also PRENATAL SCREENING OR DIAGNOSIS).... pregnancy tests

Pulmonary Function Tests

Tests to assess how the LUNGS are functioning. They range from simple spirometry (measuring breathing capacity) to sophisticated physiological assessments.

Static lung volumes and capacities can be measured: these include vital capacity – the maximum volume of air that can be exhaled slowly and completely after a maximum deep breath; forced vital capacity is a similar manoeuvre using maximal forceful exhalation and can be measured along with expiratory ?ow rates using simple spirometry; total lung capacity is the total volume of air in the chest after a deep breath in; functional residual capacity is the volume of air in the lungs at the end of a normal expiration, with all respiratory muscles relaxed.

Dynamic lung volumes and ?ow rates re?ect the state of the airways. The forced expiratory volume (FEV) is the amount of air forcefully exhaled during the ?rst second after a full breath – it normally accounts for over 75 per cent of the vital capacity. Maximal voluntary ventilation is calculated by asking the patient to breathe as deeply and quickly as possible for 12 seconds; this test can be used to check the internal consistency of other tests and the extent of co-operation by the patient, important when assessing possible neuromuscular weakness affecting respiration. There are several other more sophisticated tests which may not be necessary when assessing most patients. Measurement of arterial blood gases is also an important part of any assessment of lung function.... pulmonary function tests

Blood Sugar

See blood glucose.... blood sugar

Blood Clotting

The process of blood solidification. Clotting is important in stemming bleeding from damaged blood vessels. However, unwanted blood clotting can occur inside major blood vessels and cause a myocardial infarction (heart attack) or stroke (see thrombosis).

When a blood vessel is damaged, it constricts immediately to reduce blood flow to the area. The damage sets off a series of chemical reactions that lead to the formation of a clot to seal the injury. First, platelets around the injury site are activated, becoming sticky and adhering to the blood-vessel wall. Then, the activated platelets release chemicals, which, in turn, activate blood clotting factors. These factors, together with vitamin K, act on fibrinogen and convert it to fibrin. Strands of fibrin form a meshwork, which traps red blood cells to form a clot.

There are several anticlotting mechanisms to prevent the formation of unwanted clots. These include prostacyclin (a prostaglandin), which prevents platelet aggregation, and plasmin, which breaks down fibrin (see fibrinolysis). Blood flow washes away active coagulation factors; and the liver deactivates excess coagulation factors.

Defects in blood clotting may result in bleeding disorders.

Excessive clotting (thrombosis) may be due to an inherited increase or defect in a coagulation factor (see factor V), the use of oral contraceptives, a decrease in the level of enzymes that inhibit coagulation, or sluggish blood flow through a particular area.

Treatment is usually with anticoagulant drugs such as heparin or warfarin.... blood clotting

Autologous Blood Transfusion

See TRANSFUSION – Transfusion of blood.... autologous blood transfusion

Blood-letting

See VENESECTION.... blood-letting

Blood, Diseases Of

See ANAEMIA; LEUKAEMIA; LYMPHOMA; MYELOMATOSIS; THROMBOSIS.... blood, diseases of

Defective Blood Formation

This is the main cause of anaemia in infections. The micro-organism responsible for the infection has a deleterious e?ect upon the blood-forming organs, just as it does upon other parts of the body.

Toxins. In conditions such as chronic glomerulonephritis (see KIDNEYS, DISEASES OF) and URAEMIA there is a severe anaemia due to the e?ect of the disease upon blood formation.

Drugs. Certain drugs, such as aspirin and the non-steroidal anti-in?ammatory drugs, may cause occult gastrointestinal bleeding.... defective blood formation

Dragons Blood

Love, Protection, Exorcism, Potency... dragons blood

National Blood Authority

This body manages regional TRANSFUSION centres. Among its aims are the maintenance and promotion of blood and blood products based on a system of voluntary donors; implementing a cost-e?ective national strategy for ensuring adequate supplies of blood and its products to meet national needs; and ensuring high standards of safety and quality.... national blood authority

Circulatory System Of The Blood

The course of the circulation is as follows: the veins pour their blood, coming from the head, trunk, limbs and abdominal organs, into the right atrium of the HEART. This contracts and drives the blood into the right ventricle, which then forces the blood into the LUNGS by way of the pulmonary artery. Here it is contained in thin-walled capillaries, over which the air plays freely, and through which gases pass readily out and in. The blood gives o? carbon dioxide (CO2) and takes up oxygen (see RESPIRATION), and passes on by the pulmonary veins to the left atrium of the heart. The left atrium expels it into the left ventricle, which forces it on into the aorta, by which it is distributed all over the body. Passing through capillaries in the various tissues, it enters venules, then veins, which ultimately unite into two great veins, the superior and the inferior vena cava, these emptying into the right atrium. This complete circle is accomplished by any particular drop of blood in about half a minute.

In one part of the body there is a further complication. The veins coming from the bowels, charged with food material and other products, split up, and their blood undergoes a second capillary circulation through the liver. Here it is relieved of some food material and puri?ed, and then passes into the inferior vena cava, and so to the right atrium. This is known as the portal circulation.

The circle is maintained always in one direction by four valves, situated one at the outlet from each cavity of the heart.

The blood in the arteries going to the body generally is bright red, that in the veins dull red in colour, owing to the former being charged with oxygen and the latter with carbon dioxide (see RESPIRATION). For the same reason the blood in the pulmonary artery is dark, that in the pulmonary veins is bright. There is no direct communication between the right and left sides of the heart, the blood passing from the right ventricle to the left atrium through the lungs.

In the embryo, before birth, the course of circulation is somewhat di?erent, owing to the fact that no nourishment comes from the bowels nor air into the lungs. Accordingly, two large arteries pass out of the navel, and convey blood to be changed by contact with maternal blood (see PLACENTA), while a large vein brings this blood back again. There are also communications between the right and left atria, and between pulmonary artery and aorta. The latter is known as the ductus arteriosus. At birth all these extra vessels and connections close and rapidly shrivel up.... circulatory system of the blood

Loss Of Blood

As a result of trauma. This is perhaps the simplest example of all, when, as a result of an accident involving a large artery, there is severe haemorrhage.

Menstruation. The regular monthly loss of blood which women sustain as a result of menstruation always puts a strain on the blood-forming organs. If this loss is excessive, then over a period of time it may lead to quite severe anaemia.

Childbirth. A considerable amount of blood is always lost at childbirth; if this is severe, or if the woman was anaemic during pregnancy, a severe degree of anaemia may develop.

Bleeding from the gastrointestinal tract. The best example here is anaemia due to ‘bleeding piles’ (see HAEMORRHOIDS). Such bleeding, even though slight, is a common cause of anaemia in both men and women if maintained over a long period of time. The haemorrhage may be more acute and occur from a DUODENAL ULCER or gastric ulcer (see STOMACH, DISEASES OF), when it is known as haematemesis.

Certain blood diseases, such as PURPURA and HAEMOPHILIA, which are characterised by bleeding.... loss of blood

Peripheral-blood Stem-cell Transplants

These have almost completely replaced BONE MARROW TRANSPLANT, used to treat malignancies such as LEUKAEMIA and LYMPHOMA for the past 20 years. The high doses of CHEMOTHERAPY or RADIOTHERAPY used to treat these diseases destroy the bone marrow which contains stem cells from which all the blood cells derive. In 1989 stem cells were found in the blood during recovery from chemotherapy. By giving growth factors (cytokines), the number of stem cells in the blood increased for about three to four days. In a peripheral-blood stem-cell transplant, these cells can be separated from the peripheral blood, without a general anaesthetic. The cells taken by either method are then frozen and returned intravenously after the chemotherapy or radiotherapy is completed. Once transplanted, the stem cells usually take less than three weeks to repopulate the blood, compared to a month or more for a bone marrow transplant. This means that there is less risk of infection or bleeding during the recovery from the transplant. The whole procedure has a mortality risk of less than 5 per cent – half the risk of a bone marrow transplant.... peripheral-blood stem-cell transplants

Coughing Of Blood

See: BLEEDING (haemoptysis). ... coughing of blood

Glentona Herbal Blood Purifier

Popular blood tonic of the 1930s, 1940s and 1950s. Ingredients: Liquid Extract Liquorice 5 per cent, Infusion Gentian Co Conc 10 per cent, Infusion Senna Conc 5 per cent. And 25 per cent alcoholic extractive from Burdock 5 per cent, Red Clover 5 per cent, Queen’s root 2.5 per cent, Yellow Dock root 1.25 per cent, Poke root 2.5 per cent, Sarsaparilla 2.5 per cent. (Carter Bros) ... glentona herbal blood purifier

Tea For Blood Pressure

As a natural beverage, a cup of tea brings you many health benefits. One of them is related to blood pressure. Based on the type of tea you drink, it can help lower your blood pressure. Find out more about teas for blood pressure! Problems with blood pressure Blood pressure represents the pressure made by the circulating blood on the walls of the blood vessels. However, problems appear in the case of hypertension and hypotension. Hypertension is a medical condition caused by a high blood pressure, while hypotension is caused by a low blood pressure. Both can be treated with one of the various types of tea for blood pressure. Tea for high blood pressure If you’ve got problems with hypertension (high blood pressure), hibiscus tea can help, as it is known to lower blood pressure. You can also pick one of these herbal teas: chrysanthemum tea, flax tea, periwinkle tea, red root tea, self-heal tea, white peony root tea, valerian tea, or wild cherry bark tea. You can also drink hyssop tea, barberry tea, and rosemary tea, regardless of the blood pressure problem. These three teas will help regulate your blood pressure and reduce the risk of getting either high or low blood pressure problems. Tea for low blood pressure In the case of hypotension (low blood pressure), some of the teas you can try include lovage tea, ephedra tea, wu yi tea, cat’s claw tea, vervain tea, or wheatgrass tea. Black tea can help too, though you have to be careful with it as it has a high content of caffeine. Forbidden teas for blood pressure problems There are several teas which you should avoid drinking, no matter if you’ve got problems with high blood pressure or low blood pressure. The list of teas you shouldn’t drink includes arnica tea, black cohosh tea, gentian tea, juniper tea, lobelia tea, red ginseng tea, sage tea, stone root tea, and yohimbe tea. Also, generally it isn’t recommended to drink tea that lowers blood pressure if you’ve got hypotension, or tea that leads to high blood pressure if you’ve got hypertension. Whether you’ve got problems with high blood pressure or low blood pressure, try a more natural treatment: choose one of the many teas for blood pressure!... tea for blood pressure

Blood Culture

See culture.... blood culture

Blood Glucose

The level of glucose in the blood. Abnormally high blood glucose (sometimes called sugar) levels are an indication of diabetes mellitus. (See also hyperglycaemia; hypoglycaemia.)... blood glucose

Blood Smear

See blood film.... blood smear

Blood Transfusion, Autologous

The use of a person’s own blood, donated earlier, for blood transfusion. Autologous transfusion eliminates the slight but serious risk of contracting a serious infectious illness from contaminated blood. There is no risk of a transfusion reaction occurring as a result of incompatibility between donor and recipient blood. Up to 3.5 litres of blood can be removed and stored in several sessions at least 4 days apart and up to 3 days before planned surgery. Blood may be salvaged during surgery, filtered and returned to the circulation, reducing the need for transfusion of donated blood.... blood transfusion, autologous

Blood Purifiers

Alteratives. The blood is a fluid from which every variety of cell and tissue derives its special form of food for the repair of constant wastage resulting from functions they perform. When the blood becomes vitiated from lack of exercise, too little oxygen, debilitating personal habits and sophisticated foodstuffs the whole body suffers. The vital fluid then needs to be cleansed of its impurities. Nature’s blood purifiers are unique in the world of medicine, restoring biochemical balance and promoting healthy elimination.

Blood tonic. Decoction, tablets, tinctures or fluid extracts:– Echinacea 3; Burdock 2; Goldenseal 1. See also: ALTERATIVES. ... blood purifiers

Blood Cells

Cells, also called blood corpuscles, present in blood for most or part of their lifespan. They include red blood cells, which make up about 45 per cent by volume of normal blood, white blood cells, and platelets. Blood cells are made in the bone marrow by a series of divisions from stem cells.

Red blood cells (also known as RBCs, red blood corpuscles, or erythrocytes) transport oxygen from the lungs to the tissues (see respiration). Each is packed with haemoglobin, enzymes, minerals, and sugars. Abnormalities can occur in the rate at which RBCs are either produced or destroyed, in their numbers, and in their shape, size, and haemoglobin content, causing forms of

anaemia and polycythaemia (see blood, disorders of).

White blood cells (also called WBCs, white blood corpuscles, or leukocytes) protect the body against infection and fight infection when it occurs. The 3 main types of are granulocytes (also called polymorphonuclear leukocytes), monocytes, and lymphocytes. Granulocytes are further classified as neutrophils, eosinophils, or basophils, and each type of granulocyte has a role in either fighting infection or in inflammatory or allergic reactions. Monocytes and lymphocytes also play an important part in the immune system. Lymphocytes are usually formed in the lymph nodes. One type, a T-lymphocyte, is responsible for the delayed hypersensitivity reactions

White (see allergy) and Red blood blood cell is also involved in cell (neutrophil) protection against cancer. T-lymphocytes manufacture chemicals, known as lymphokines, which affect the function of other cells. In addition, the T-cells moderate the activity of B-lymphocytes, which form the antibodies that can prevent a second attack of certain infectious diseases. Platelets (also known as thrombocytes), are the smallest blood cells and are important in blood clotting.

The numbers, shapes, and appearance of the various types of blood cell are of great value in the diagnosis of disease (see blood count; blood film).... blood cells

Blood, Disorders Of

Disorders resulting from abnormalities in any of the components of blood or from infection. Disorders include types of anaemia, polycythaemia, bleeding disorders, and unwanted clot formation (thrombosis), hypoalbuminaemia (albumin deficiency) and agammaglobulinaemia (deficiency of gamma-globulin). Blood disorders such as sickle cell anaemia, thalassaemia, and haemophilia are inherited. Bone marrow cancers that affect production of blood components include leukaemia, polycythaemia vera, and multiple myeloma. Blood poisoning is usually due to septicaemia or a toxin such as carbon monoxide. Some drugs can cause blood abnormalities as a side effect. (See also anaemia, haemolytic; anaemia, iron-deficiency; anaemia, megaloblastic; malaria; hyperbilirubinaemia.)... blood, disorders of

Blood Vessels

A general term given to arteries, veins, and capillaries (see circulatory system).... blood vessels

Coagulation, Blood

The main mechanism by which blood clots are formed, involving a complex series of reactions in the blood plasma (see blood clotting).... coagulation, blood

Faeces, Blood In The

See faeces, abnormal; rectal bleeding.... faeces, blood in the

Kidney Function Tests

Tests performed to investigate kidney disorders.

Urinalysis is a simple test in which a urine sample is examined under a microscope for blood cells, pus cells, and casts (cells and mucous material that accumulate in the tubules of the kidneys and pass into the urine).

Urine may be tested for substances, such as proteins, that leak into the urine when the kidneys are damaged.

Kidney function can be assessed by measuring the concentration in the blood of substances, such as urea and creatinine, that the kidneys normally excrete.

Kidney function may also be assessed by kidney imaging techniques.... kidney function tests

Liver Function Tests

Tests of blood chemistry that can detect changes in the way the liver is making new substances and breaking down and/or excreting old ones.

The tests can also show whether liver cells are healthy or being damaged.... liver function tests

Blood Donation

The process of giving blood for use in blood transfusion.

Donated blood is tested for a range of infectious agents such as hepatitis B and hepatitis C and antibodies to HIV. After being classified into blood groups, the blood is stored in a blood bank, either whole or separated into its different components (see blood products). Apheresis is a type of blood donation in which only a specific blood component, such as plasma, platelets, or white cells, is withdrawn from the donor. blood film A test that involves smearing a drop of blood on to a glass slide for examination under a microscope. The blood film is stained with dyes to make the blood cells show up clearly.

The test allows the shape and appearance of blood cells to be checked for any abnormality, such as the sickleshaped red blood cells characteristic of sickle cell anaemia.

The relative proportions of the different types of white blood cells can also be counted.

This examination, called a differential white cell count, may be helpful in diagnosing infection or leukaemia.

Blood films are also used in diagnosing infections, such as malaria, in which the parasites can be seen inside the red blood cells.

Blood films are usually carried out together with a full blood count.... blood donation

Blood Products

Donated blood that is separated into its various components: red cells, white cells, platelets, and plasma (see blood donation). Each blood product has a specific lifespan and use in blood transfusion. Packed red cells (blood with most of the plasma removed) are used to treat patients with some forms of chronic anaemia and babies with haemolytic disease of the newborn. Washed red cells (with white blood cells and/or plasma proteins removed) are used when a person needs repeated transfusions because there is less risk of an allergy to any of the blood components developing.

Platelets may be given in transfusions for people with blood-clotting disorders. Patients who have life-threatening infections may be treated with granulocytes, a type of white blood cell. Fresh frozen plasma is used to correct many types of bleeding disorder because it contains all the clotting factors. Albumin, prepared from the plasma of whole blood, is used mainly to treat shock resulting from severe blood loss until compatible whole blood becomes available. Purified albumin preparations are used to treat nephrotic syndrome and chronic liver disease.

Concentrates of blood clotting factors and are used in the treatment of haemophilia and Christmas disease.

Immunoglobulins (also called antibodies), which are extracted from blood plasma, can be given by injection (see immunoglobulin injection) to protect people who are unable to produce their own antibodies or have already been exposed to an infectious agent, or to provide short-term protection against hepatitis A.

Immunoglobulins are given in large doses to treat certain autoimmune disorders.... blood products

Blood Tests

Analysis of a sample of blood to give information on its cells and proteins and any of the chemicals, antigens, antibodies, and gases that it carries. Such tests can be used to check on the health of major organs, as well as on respiratory function, hormonal balance, the immune system, and metabolism. Blood tests may look at numbers, shape, size, and appearance of blood cells and assess the function of clotting factors. The most important tests are blood count and blood group tests if transfusion is needed. Biochemical tests measure chemicals in the blood (see acid–base balance; kidney function tests; liver function tests). Microbiological tests (see immunoassay) look for microorganisms that are in the blood, as

in septicaemia. Microbiology also looks for antibodies in the blood, which may confirm immunity to an infection. blood transfusion The infusion of large volumes of blood or blood products directly into the bloodstream to remedy severe blood loss or to correct chronic anaemia. In an exchange transfusion, nearly all of the recipient’s blood is replaced by donor blood. Before a transfusion, a sample of the recipient’s blood is taken to identify the blood groups, and it is matched with suitable donor blood. The donor blood is transfused into an arm vein through a plastic cannula. Usually, each unit (about 500 ml) of blood is given over 1–4 hours; in an emergency, 500 ml may be given in a couple of minutes. The blood pressure, temperature, and pulse are monitored during the procedure.

If mismatched blood is accidentally introduced into the circulation, antibodies in the recipient’s blood may cause donor cells to burst, leading to shock or kidney failure. Less severe reactions can produce fever, chills, or a rash. Reactions can also occur as a result of an allergy to transfused blood components. All

blood used for transfusion is carefully screened for a number of infectious agents, including HIV (the AIDS virus) and hepatitis B and hepatitis C.

In elderly or severely anaemic patients, transfusion can overload the circulation, leading to heart failure.

In patients with chronic anaemia who need regular transfusion over many years, excess iron may accumulate (haemosiderosis) and damage organs such as the heart, liver, and pancreas.

Treatment with desferrioxamine to remove excess iron may be needed.... blood tests

Lung Function Tests

See pulmonary function tests.... lung function tests

Occult Blood, Faecal

The presence in the faeces of blood that cannot be seen by the naked eye, but can be detected by chemical tests. Such tests are widely used in screening for cancer of the colon (see colon, cancer of). Faecal occult blood may also be a sign of a gastrointestinal disorder such as oesophagitis, gastritis, or stomach cancer; cancer of the intestine (see intestine, cancer of); rectal cancer (see rectum, cancer of); diverticular disease; polyps in the colon; ulcerative colitis; or irritation of the stomach or intestine by drugs such as aspirin. (See also rectal bleeding.)... occult blood, faecal

Personality Tests

Questionnaires designed to define various personality traits or types. Tests may be designed to detect psychiatric symptoms, underlying personality traits, how outgoing or reserved a person is, and predisposition to developing neurotic illness.... personality tests

Respiratory Function Tests

See pulmonary function tests.... respiratory function tests

Semen, Blood In The

A usually harmless condition in which a small amount of blood is present in the semen.

Occasionally, there is an underlying cause (such as an infection or, very rarely, cancer) that requires treatment.

Blood in the semen may also occur after a prostate biopsy.... semen, blood in the

Coughing Up Blood

A symptom, medically known as haemoptysis, that is caused by rupture of a blood vessel in the air-ways, lungs, nose, or throat. The coughed-up blood may appear as brightred or rusty-brown streaks, clots in the sputum, a pinkish froth, or, more rarely, blood alone. In all cases, medical assessment is needed. Many disorders can cause haemoptysis. The most common are infections, such as pneumonia or bronchitis; and congestion in and rupture of blood vessels in the lungs due to heart failure, mitral stenosis, or pulmonary embolism. A cancerous tumour can also produce haemoptysis by eroding the wall of a blood vessel.

Investigations into coughing up blood include chest X-ray, and, in some cases, bronchoscopy. In about a 3rd of cases, no underlying cause is found. Treatment depends on the cause.... coughing up blood

Hearing Tests

Tests carried out to assess hearing. Hearing tests are performed as part of a routine assessment of child development and when hearing impairment is suspected. The tests are sometimes included in a general medical examination. Hearing tests may also be used to identify the cause of tinnitus or dizziness.

An audiometer (an electrical instrument) is used to test an individual’s ability to hear sounds at different frequencies and volumes. The lowest level at which a person can hear and repeat words (the speech reception threshold) is tested, as is the ability to hear words clearly (speech discrimination). The type of hearing loss (see deafness) is determined by holding a tuning fork to different parts of the ear.... hearing tests

Intelligence Tests

Tests designed to provide an estimate of a person’s mental abilities. The most widely used are Wechsler tests of which there are 2 basic types: the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler Intelligence Scale for Children (WISC). Each is divided into verbal (concerned with language skills) and performance sections, including measures of constructional ability and visual-spatial and perceptual ability (interpretation of shapes). Other tests include the Stanford–Binet test, which is used mainly as a measure of scholastic ability.

In most intelligence tests, scoring is based on mental age (MA) in relation to chronological age (CA). The intelligence quotient (IQ) is MA divided by CA, multiplied by 100. The tests are devised to ensure that 3 in 4 people have an IQ between 80 and 120. They are standardized so that the score indicates the same relative ability at different age levels.

Intelligence tests may be used to assess school or job aptitude. However, they have been criticized for their alleged bias regarding gender and race.... intelligence tests

Skin Tests

Procedures for determining the body’s reaction to various substances by injecting a small quantity of the substance under the skin or by applying it to the skin (usually on patches).

Patch tests are used in the diagnosis of contact allergic dermatitis.

They can also be used to test immunity to certain infectious diseases (such as in the tuberculin test).... skin tests

Tests, Medical

Tests may be performed to investigate the cause of symptoms and establish a diagnosis, to monitor the course of a disease, or to assess response to treatment. A medical testing programme carried out on apparently healthy people to find disease at an early stage is known as screening.

The accuracy of a test is based on its sensitivity (ability to correctly identify diseased subjects), specificity (ability to correctly identify healthy subjects), and predictive value.

The predictive value is determined by a mathematical formula that involves the number of accurate test results and the total number of tests performed.

The best tests have both high specificity and high sensitivity, and therefore high predictive value.... tests, medical

Thyroid-function Tests

A group of blood tests used to evaluate the function of the thyroid gland and to detect or confirm any thyroid disorder. The thyroid hormones T3 and T4 are measured, as well as thyroid-stimulating hormone (TSH), the pituitary gland hormone that stimulates the thyroid gland.... thyroid-function tests

Tuberculin Tests

Skin tests used to determine whether or not a person has been exposed to the bacterium that causes tuberculosis. Tuberculin tests are carried out for diagnosis of tuberculosis, and before BCG vaccination. A small amount of tuberculin (purified protein from the bacteria) is injected into the skin. A few days later, the skin reaction, if any, is noted. A reaction indicates previous exposure.... tuberculin tests

Tuning Fork Tests

Hearing tests carried out to diagnose conductive deafness. In the Weber test, a vibrating tuning fork is held against the forehead. If there is conductive hearing loss, the sound seems louder in the affected ear. In the Rinne test, a vibrating tuning fork is held first near the ear, and then against the bone behind it. If it sounds louder when held against the bone, there is conductive hearing loss.... tuning fork tests

Urine Tests

See urinalysis.... urine tests

Blood Cell

(blood corpuscle) any of the cells that are present in the blood in health or disease. The cells may be subclassified into three major categories, namely red cells (*erythrocytes); white cells (*leucocytes), which include granulocytes, lymphocytes, and monocytes; and *platelets (see illustration). The blood cells account for approximately 40% of the total volume of the blood in health; red cells comprise the vast majority.... blood cell

Donor’s Blood Group

Blood group of people donor can receive blood from... donor’s blood group

Blood Plasma See Plasma.

... blood plasma see plasma.

Blood Serum

see serum.... blood serum

Vomiting Blood

A symptom of bleeding from within the digestive tract. Vomiting blood may be caused by a tear in the lower oesophagus (see Mallory–Weiss syndrome), bleeding from oesophageal varices, erosive gastritis, peptic ulcer, or, rarely, stomach cancer. Blood can also be vomited if it is swallowed during a nosebleed. Vomited blood may be dark red, brown, black, or may resemble coffee grounds. Vomiting of blood is often accompanied by the passing of black, tarry faeces.

The cause of vomiting blood is investigated by endoscopy of the oesophagus and stomach, or by barium X-ray examinations. If blood loss is severe, blood transfusion, and possibly surgery to stop the bleeding, may be required.... vomiting blood

Blood Coagulation

(blood clotting) the process whereby blood is converted from a liquid to a solid state. The process may be initiated by contact of blood with a foreign surface (intrinsic system) or with damaged tissue (extrinsic system). These systems involve the interaction of a variety of substances (*coagulation factors) and lead to the production of the enzyme thrombin, which converts the soluble blood protein *fibrinogen to the insoluble protein *fibrin, forming the blood clot. Finally, fibrin is broken down by the action of *plasmin. Anticoagulants and tissue plasminogen activators act by inhibiting or activating various pathways in this cascade (see illustration). Blood coagulation is an essential mechanism for the arrest of bleeding (*haemostasis). See also platelet activation.... blood coagulation

Blood Group

any one of the many types into which a person’s blood may be classified, based on the presence or absence of certain inherited antigens on the surface of the red blood cells. Blood of one group contains antibodies in the serum that react against the cells of other groups.

There are more than 30 blood group systems, one of the most important of which is the ABO system. This system is based on the presence or absence of antigens A and B: blood of groups A and B contains antigens A and B, respectively; group AB contains both antigens and group O neither. Blood of group A contains antibodies to antigen B; group B blood contains anti-A antibodies or *isoagglutinins; group AB has neither antibody and group O has both. A person whose blood contains either (or both) of these antibodies cannot receive a transfusion of blood containing the corresponding antigens. The table illustrates which blood groups can be used in transfusion for each of the four groups.

Blood group... blood group

Bolam And Bolitho Tests

where clinical *negligence is claimed, tests used to determine the standard of care owed by professionals to those whom they serve, e.g. the standards of care provided to patients by doctors. The 1957 case of Bolam v Friern Hospital Management Committee established that if a doctor acts in accordance with a responsible body of medical opinion, he or she will not be negligent. In 1997 this standard of care test was amended by the case of Bolitho v City and Hackney Health Authority, which requires the doctor’s behaviour to satisfy the judgment not only of responsible medical opinion but also of a court’s own independent logical analysis.... bolam and bolitho tests

Clotting Factors

see coagulation factors.... clotting factors

Dexamethasone Suppression Tests

(DSTs) tests based on the principle that appropriate doses of *dexamethasone can suppress the output of cortisol from the adrenal glands in the normal state and that this ability is reduced or lost in *Cushing’s syndrome. In the overnight DST 1 mg of dexamethasone is administered at midnight and the serum cortisol level is measured at 9.00 am the next morning. Failure to suppress cortisol output may indicate Cushing’s syndrome but also occurs in patients with obesity and depressive illness. In the low-dose DST (0.5 mg dexamethasone every 6 hours for 48 hours), cortisol suppression occurs in patients with obesity and depression but not in those with Cushing’s syndrome. In the high-dose DST (2 mg dexamethasone every 6 hours for 48 hours), cortisol is suppressed in patients with Cushing’s disease (in which excess amounts of ACTH are secreted by the pituitary gland) but not in those with Cushing’s syndrome due to other causes. Although the low- and high-dose tests are unreliable, all three tests should be performed to aid the diagnosis of Cushing’s syndrome.... dexamethasone suppression tests

Faecal Occult Blood Test

(FOBT) a noninvasive test used to identify microscopic blood (see occult) in faeces. It is widely used as a screening test for colorectal cancer.... faecal occult blood test

Heel-prick Blood Test

see Guthrie test.... heel-prick blood test

Nhs Blood And Transplant

(NHSBT) a *special health authority established in 2005 to provide a safe and reliable supply of blood, organs, stem cell services, and diagnostics to hospitals. NHSBT also provides specialist therapeutic apheresis services, which remove or replace a single component of blood (e.g. malignant white cells or low-density lipoprotein), at six sites in England.

NHS Blood and Transplant website... nhs blood and transplant

Renal Function Tests

tests for assessing the function of the kidneys. These include measurements of the specific gravity of urine, creatinine *clearance time, and blood urea levels; intravenous urography; and renal angiography.... renal function tests

Stycar Tests

Standard Tests for Young Children and Retardates: tests to detect visual problems in children between the ages of six months and five years. They consist of a series of standardized balls, toys, or letters. The tests were developed by the paediatrician Mary Sheridan.... stycar tests

Synacthen Tests

tests used to assess the ability of the adrenal cortex to produce cortisol. Serum cortisol is measured before and then 30 minutes (or 5 hours) after an intramuscular injection of 250 ?g (or 1 mg) tetracosactide (Synacthen), an analogue of *ACTH. The adrenal glands are considered to be inadequate if there is a low baseline concentration of cortisol or the rise is less than a certain predefined amount.... synacthen tests

Umbilical Cord Blood Banked Stem Cells

haemopoietic *stem cells collected from umbilical cord blood donated at birth, which can be stored indefinitely and used if a sibling or any other blood-compatible baby develops an illness (such as leukaemia) that could only be treated by cord-blood stem-cell transplantation. This facility is now available in the UK and the USA.... umbilical cord blood banked stem cells



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