Glossary

Abstract

The entries are defined and described mainly from the perspective of transfusion medicine. Additional entries that do not necessarily appear in the text may be included; others within the text may have been omitted from this glossary. Some entries are cross-referenced; other entries are ‘opposites’, such as acute and chronic, or ‘relate’ to each other, such as immunodiffusion and precipitation, and although separately defined and described, these entries are flagged in the subject title as ‘see also’. 2,3 disphosphoglycerate (2,3 DPG) is present in red cells and together with haemoglobin, controls the amount of oxygen released to the tissues of the body. 2,3 DPG levels deteriorate in stored red cells which then lose their ability to release oxygen rapidly at tissue level. Post-transfusion, it takes about 24 hours for the 2,3 BPG in stored red cells to fully regain functionality. 2-mercaptoethanol (2-ME) is a reducing agent used to differentiate between IgM and IgG antibodies. When mixed with serum containing IgM antibodies, some of the disulphide bonds are broken. As a result, the IgM antibodies become less efficient or lose their ability to agglutinate red cells carrying the corresponding antigen. 2-ME is extremely strong smelling and to minimise inhalation it should be used only in a well-ventilated area apart from other personnel. 2-ME may cause irritation of the eyes, skin and respiratory tract, so protective clothing should be worn. Safety protocols for the storage of potentially harmful chemicals should be followed. This may be viewed from the occupational safety angle or from the perspective of transfusion. An accident is an unplanned event with an unfavourable outcome. For example, a brick falls from the building site, hitting an individual on the head, or a unit of blood intended for another patient is accidentally transfused. This is the process whereby an agency evaluates an organisation against a predetermined set of documented standards, and, if the organisation meets or exceeds the standards, accredits the organisation. Acid citrate dextrose (ACD) is an anticoagulant solution containing citric acid (A), sodium citrate (C) and dextrose (D). Acquired immune deficiency syndrome (AIDS) is the result of untreated infection with the human immunodeficiency virus (HIV). Individuals who are seropositive become prone to infections. This is because the ability of the immune system to overcome micro-organisms becomes increasingly impaired by the actions of HIV. If an opportunistic infection such as tuberculosis (TB), hepatitis B, shingles or CMV is contracted, there is a serious impact on health and such an infection may become life-threatening. When the medical condition of the patient is termed acute, it means that it is of sudden onset. For example, hypovolaemic shock may be the result of sudden haemorrhage. This is the deliberate reduction in the amount of haemoglobin in the blood, usually by the withdrawal of whole blood from a patient just prior to elective surgery. Blood volume is restored, but the number of circulating red cells is reduced. After surgery, the blood that was withdrawn may be re-infused if needed, and this prevents the use of allogeneic blood, which may be considered less safe. Red cells separated from whole blood collected in CPD are suspended in an additive solution such as AS-3 for improved storage and shelf life extended up to 42 days. Breakdown of ATP provides the energy required by cells to carry out energy requiring processes. Energy rich compounds (such as glucose or dextrose) are taken into the cell, and enzymes break them down to release their potential energy. The released energy must be stored in a form that the cell can utilise, and this is known as ATP. An adjuvant is a substance that may stimulate the immune system to enhance its response to an immunogen, increasing the speed and intensity of the response to a smaller dose of immunogen, without altering its nature. This is the process by which an antibody is removed from serum/plasma through the addition of red cells carrying the corresponding antigen. Serum/plasma that has been rendered free of antibody in this way is said to have been adsorbed. Red cells that have bound an antibody from serum/plasma are said to have adsorbed that antibody. The term adsorb should be used in this context and not the term absorb. This term means ‘without globulin’. Patients with agammaglobulinaemia have an absence of serum immunoglobulin and this causes primary immunodeficiency. It may be sex-linked or inherited because of an autosomal gene and may be of early or late onset. Patients suffer recurrent infections, and often have chronic respiratory tract disease. Prophylactic, chronic treatment with intravenous immunoglobulin is usually helpful. Hypogammaglobulinaemia is the term used to describe a condition in which the amount of serum immunoglobulin is reduced rather than absent. In the laboratory, this is a visible clumping reaction that may be seen with the naked eye when an antibody in the serum/plasma binds to its specific antigen. The reaction is called haemagglutination when the antigen in found on a red blood cell, but the term agglutination is often used when referring to red cell agglutination. A substance that makes particles (such as red cells) for which it is specific, clump together or agglutinate in a visible way, is called an agglutinin. For example, anti-A (in the ABO blood group system) is an agglutinin. This is a protein extracted (fractionated) from human plasma and used in place of whole plasma for the treatment of shock and burns or to restore blood volume. It is pasteurised to make it a viral-safe product. An allele is one of the alternate genes in a series of genes at the same locus. Each individual inherits two alleles for each gene at each autosomal locus, one from each parent. For example, A and B are alleles. Normally the gene products, expressed in terms of red cell antigens, are termed antithetical. This is a substance with which the corresponding antibody reacts (usually of the IgE class of immunoglobulin) to cause an allergic reaction in the host. For example, pet dander or pollen is an allergen and causes a reaction, such as hay fever in those with the allergy to the specific substance. Immunoglobulin that is produced against an antigen that is foreign to the individual, but in the same species. This is blood that is collected from a different member of the same species. Blood banks store allogeneic blood as available stock. Alloimmunisation is the production of antibodies in an individual against the antigens of another individual of the same species. For example, a patient who is negative for the K antigen may become alloimmunised to K when transfused with K positive blood. Another older term that is sometimes used is isoimmunisation. This is a process whereby a small sample of amniotic fluid is withdrawn from the sac surrounding the fetus in the uterus of a pregnant woman, in order to carry out tests to determine medical information about the fetus. This is the fluid that surrounds the fetus in utero. It supports and protects the fetus, allowing it to move around as it grows and develops. Amniotic fluid may be sampled to test for various conditions, such as the karyotyping of fetal epithelial cells to determine genetic information, or the measurement of bilirubin levels to determine the severity of haemolytic disease. An amorph is an allele that has no apparent gene product. For example, in the genes controlling the ABO antigens, the O gene does not result in a specific antigen being found on the red cells and may be referred to as an amorph. This is the term used to describe a reduction in the number of circulating red blood cells and/or in the level of haemoglobin. This is the memory response of the immune system when it has been primed (exposed) to an immunogen in the past, and when the same immunogen is presented again, there is a recall response to produce antibodies more rapidly than if the immunogen was being encountered for the first time. This is a severe allergic reaction that occurs with subsequent exposure to an immunogen that initially stimulated the production of immunoglobulin E (IgE) antibodies. This type of immune reaction leads to the release of powerful chemicals that cause vasodilatation, a drop in blood pressure and swelling of the bronchial tubes. This causes restrictions to breathing and may be life-threatening without medical intervention. Anaphylactoid reactions resemble anaphylactic reactions clinically but are not caused by an IgE-mediated immune response. The two terms are sometimes used interchangeably. A unit of length equal to 10−10 m. The antenatal period refers to the time during which the female is pregnant. The word antenatal literally means before birth. During the immune response, antibodies that are able to react specifically with the foreign immunogens that stimulated their production are formed in the blood, with a view to destroying those specific immunogens. An alloantibody is specific for an antigen within the same species; an autoantibody is directed towards self, and a heterophile antibody is directed towards an antigen in another species. An anticoagulant is a solution that prevents blood from clotting. Anticoagulants such as ACD and CPDA-1, used in the collection of donor blood, must be non-toxic in order to be safely transfused along with blood. Donated blood usually has additional preservatives added to assist in the storage of the blood and allow for a longer shelf life. An antigen is a substance that, although it is able to combine with specific antibody, does not provoke an immune response unless it is immunogenic. Although the terms antigen and immunogen are often viewed as synonyms, the term immunogen is correctly used in the place of antigen to describe a substance that stimulates the production of antibodies by the immune system. This is a cell that attaches to antigenic epitopes and locks them onto its surface. The antigen-presenting cell then transports the captured antigen to other cells within the immune system that can initiate an antibody response. In other words, the antigen is ‘presented’ to immunocompetent cells for their response. AHF is an older term for clotting factor VIII. It can be extracted from fresh frozen plasma by the fractionation process and is used to replace factor VIII in those with FVIII deficiency, such as individuals with haemophilia A. It may also be produced using recombinant technology without human plasma as a starting material. Antihuman globulin (AHG) consists of antibodies that are directed against human proteins. This reagent was originally produced by injecting human immunoglobulin or human complement into animals of a different species, such as rabbits or goats, to stimulate the production of antibodies. Once the AHG is standardised, it is used in laboratory tests to bring about the agglutination of red cells sensitised either with IgG antibodies or complement. AHG is now manufactured using monoclonal production technology. This is the term commonly used for a blood grouping reagent containing specific red cell antibodies. Antibodies in antiserum against bacteria or viruses can bind with the infectious agent. This term describes the failure of the kidneys to produce urine. It is one of the signs of a haemolytic transfusion reaction, in which the kidneys may be damaged. This refers to the automated process whereby whole blood is taken from the donor (while he/she is attached to the apheresis machine) and then immediately processed by the machine to harvest a selected component and re-infuse the rest. The machine is programmed according to the component of blood to be harvested, such as plasma or platelets. This is a lectin derived from groundnuts (peanuts) that will detect T-activation of red cells. Red cells may become T-activated when their surfaces are eroded by the action of bacteria. This is a procedure used to evaluate the performance and effectiveness of a system, such as an organisation's quality management system. Attenuated literally means weakened. This is a term used to describe a micro-organism that has been weakened or ‘subdued’ by a laboratory process, while maintaining its immunogenic properties. Attenuated strains of viruses may be used to inoculate or vaccinate individuals to produce antibodies and become immune without causing illness. A quality audit is an independent evaluation in order to assess whether the operational activities of an organisation comply with the documented and planned provisions, such as the organisation's quality policy, operating procedures, general policies and any applicable legislation. Autoimmune haemolytic anaemia (AIHA) is an anaemia caused by the action of autoantibodies, or antibodies against self. The red cells of the individual become sensitised and this may result in their reduced lifespan, leading to anaemia. This is a control carried out (in parallel with laboratory tests) on the red cells and serum/plasma of an individual. There should be no reaction in this control for the test results carried out at the same time, to be valid. When patients scheduled for elective surgery can donate and later receive their own blood during or after the operation, this is referred to as autologous transfusion. An autoimmune disease occurs when the immune system fails to recognise one of more of the host's tissues as “self” and mounts an immune attack on that tissue. Examples are autoimmune haemolytic anaemia (AIHA) and systemic lupus erythematosus (SLE). An autosome is any one of the chromosomes that are not involved in the determination of sex and are alike in both males and females. Humans have 22 pairs of autosomes. This describes an antiseptic solution or biological substance (e.g. white cells or plasma) that can kill bacteria. One of the waste products of haemoglobin breakdown is called bilirubin. It is a yellow-pigmented substance that gives newborn infants suffering from haemolytic disease of the fetus and newborn or physiological jaundice their characteristic jaundiced (yellow) colour. The responsibility for collection, testing, processing and provision of safe blood for transfusion, within a defined area, region or country, is that of the blood service. The blood bank is the depot/laboratory in the hospital, where blood and blood products are stored prior to issue, and is part of the hospital transfusion service. Some products, such as red blood cells, must be crossmatched for specific patients before transfusion, to ensure that blood is compatible. These tests are usually the blood bank's responsibility. Blood components are those therapeutic parts of whole blood that are prepared by centrifugation, separation and specialised storage and which are prescribed specifically according to patients' needs. They may also be collected by apheresis. A blood group system is comprised of one or more blood group antigens controlled at a single genetic locus or by two or more closely linked alleles. This is any therapeutic product derived from blood or plasma. Products include plasma, red cells, platelets, and cryoprecipitate, which are derived from whole blood and sometimes called fresh components. Plasma contains different proteins such as albumin, fibrinogen, immunoglobulin, and clotting factors, some of which are separated by fractionation techniques. This is a laboratory reagent that is used as a potentiator for the agglutination of sensitised red cells. This is a proteolytic enzyme extracted from pineapples and used in blood group serology to enhance certain sensitisation/agglutination reactions. After centrifugation, the BC is the layer of white cells and platelets that is seen between the red cells (at the bottom) and the plasma (at the top) of anticoagulated blood. Calibration is the comparison of a standard or instrument against one of certified accuracy in order to detect and quantify any inaccuracy, and the process whereby the standard or instrument is adjusted to compensate for the inaccuracy. Laboratory equipment is adjusted to perform according to such a reference standard (e.g. a centrifuge rpm meter reading is adjusted to the actual speed of the rotor measured with an approved device, or the mass reading of a scale is set to match the mass of a certified set of standard weights). An external service agent usually performs the calibration at preset time intervals (often annually). Written records of calibration should be kept. A broad term used for any disease that results from cellular changes that cause the uncontrolled division and growth of cells. A large group of organic compounds, including sugars, starches and cellulose. The A and B antigens of the ABO blood group system are examples of carbohydrate antigens. As foodstuff, carbohydrates are broken down to release energy in the human body, Special machines, called centrifuges, are used to centrifuge or ‘spin’ the blood bags (or specimen tubes) around at high speed, using centrifugal force to separate the components of the sample mixture based on differences in density or mass. The bags (or tubes) are placed in the centrifuge in buckets that swing out to a horizontal position when the centrifuge is centrifuging or ‘spinning’. In so doing, the heaviest particles (red cells) are forced furthest away from the central spindle. This means that they are forced to the bottom of the bag or tube. The buffy coat of lighter platelets and white cells settles above the red cells and the plasma remains on the top. Trypanosoma cruziis a parasite transmitted by reduviid bugs that live in Central and South America. The actual bite does not transfer the parasite; when the bite itches and the host scratches it, the infected faeces that the bug has deposited on the skin are able to enter the host, either via the bite site or by hand contact transfer to the eyes or mouth. The disease may also be spread from accidentally ingesting infected bugs, by placental transfer of parasites from mother to fetus, or by transfusion. A nonspecific term for a chemical agent which carries out a reaction or process. For example, chemical mediators such as histamine and serotonin increase vascular permeability and play an important role in the inflammatory response. Chemokines are small cytokines, or signalling proteins, that are secreted by cells and are able to induce chemotaxis in nearby cells of the immune system. This virus is spread to humans by infected mosquitoes and outbreaks have occurred in Africa (mainly Central and Southern Africa), South America, Asia and parts of Europe. Symptoms include fever, joint pain, headache, and rash. A chimera is an individual or organism whose cells are derived from two or more zygotes. Twin chimerism in humans occurs when some of the haemopoietic stem cells of one twin crosses over and develops in the bone marrow of the other twin. The blood of each of the twins may then contain a mixture of their own blood and that of the other twin. If the blood groups of the twins are different this may result in mixed field agglutination being detected in laboratory tests – the individual may appear to have two blood groups. Chimerism may also be seen after a bone marrow transplant. A chromosome is the threadlike strand of DNA and other proteins found in the nucleus of animal and plant cells, and on which the genes are located. Chromosomes play a role in the passing on of hereditary information. A chronic medical condition is one which persists or is ongoing over a prolonged period of time. This is an anticoagulant solution containing citric acid, sodium citrate (C), sodium phosphate (P), dextrose (D) and adenine (A). The amounts used in the formulation vary and variations are indicated by the number at the end, in this case ‘1’. These are cells that are genetically identical in every way and are derived from a single ancestor. A colony of bacteria developed by asexual cell division is an example of a clone. In the blood donation procedure, the venepuncture site on the donor's arm is thoroughly cleaned and the sterile needle on the end of the blood bag tubing is inserted into the vein of the donor. In this way a direct connection is made between the donor's circulation and the sterile blood pack. At the end of the donation the blood bag tubing is sealed, and the contents of the blood bag should be free of any bacterial contamination. Once the blood bag has been sealed it is considered to be a closed system and the integrity of the product is ensured while the system remains closed. Blood normally clots soon after being shed, or after collection into a test tube or container, unless an anticoagulant is added. There are 13 different proteins or other substances that comprise the clotting factors in the plasma, all of which are essential if normal clotting is to occur. These are the clotting factors. Coagulation Blood does not normally coagulate in vivo. The coagulation mechanism must be triggered for the coagulation cascade to commence, at the end of which coagulation or clotting occurs. Blood coagulation is the culmination of a series of complex reactions that follows one of two pathways initially; the extrinsic pathway (tissue damage) or the intrinsic pathway (contact activation). This is followed by a common pathway, and the remaining clotting factors activated, after which a clot is formed. Genes are co-dominant if both alleles are expressed equally when both are present. For example, in the ABO system the alleles A and B are co-dominant and when both are present, the red cells will carry both A and B antigens and the individual will be group AB. Management of storage conditions relating to the maintenance of temperature from the time of blood collection, through processing, testing, labelling, to transfusion into a patient is known as ‘cold chain management’. These are intravenous fluids that contain large molecular mass molecules in suspension, such as proteins or large glucose polymers. Colloids do not pass through the capillary membranes into the tissues and therefore raise the osmotic pressure of blood. Colloids are either extracted from plasma (albumin) or are produced synthetically, such as dextrose starches (hydroxyethyl starches or HES), dextran and gelatines. A blood product is said to be compatible if it causes no adverse reaction in the recipient and if all the transfused components function and survive as expected. Compatibility between donated blood and the blood of an intended recipient is indicated when there is no observable reaction using appropriate laboratory tests with the serum/plasma of the patient and with the red cells of the donation intended for transfusion. Complement plays a role in immune defence and consists of a series of alpha, beta and gamma globulins that are present in all normal sera. Some antibodies activate complement once they have complexed with antigen. Activation of the complement pathway serves as the effector mechanism by which cells coated with complement components are removed from the circulation by macrophages or are immediately destroyed (ruptured or lysed). This is the process of evaluating that computer programs, together with the computer hardware as configured in the local environment, conform to the specified requirements and perform as expected under all circumstances. Solutions with the ability of absorbing heat at a particular melting point are used as coolants in blood/component transport containers. The selected coolant reaches its melting point and then stays at that temperature for long periods as it is converting from solid phase to liquid phase, thus maintaining the blood/component temperature close to its melting point. The Coombs' test is an historical term for the antihuman globulin test, named after one of the scientists (Coombs) who together with Mourant and Race introduced the technique into laboratory use in 1945, although it was discovered many years earlier in 1908 by Moreschi. Copper sulphate (CuSO4) solution is used to qualitatively assess Hb levels of prospective blood donors. The solution is designed to be used with finger-prick samples of blood. Provided that the drop of blood added to the solution sinks to the bottom of the container within about 10 seconds, the individual has a sufficiently high Hb level to give a donation of blood. Failing the CuSO4 test does not necessarily mean that the individual is anaemic, but that the Hb level is not high enough to safely donate blood. These are red cells derived from the umbilical cord at delivery of an infant. A cord blood sample is taken to test the blood of the newborn. The procedure whereby a fetal blood sample is drawn, antenatally, from the umbilical cord. Ultrasound is used to determine the position of the fetus and the umbilical cord. These are measures that are taken to correct conditions that are impacting adversely on quality in order to eliminate an existing cause of non-conformity. Creutzfeldt-Jakob disease (CJD) is a type of transmissible spongiform encephalopathy (TSE). These diseases are caused by prions which are misfolded proteins found (as the result of a disease process) in the body. They can transmit their misfolded shape onto normal protein. Their presence in the body leads to several types of fatal neurodegenerative disease, including familial CJD, sporadic CJD, iatrogenic CJD (caused by contaminated instruments or substances, such as human growth hormone), and variant CJD (vCJD). vCJD in humans is caused by the ingestion of cattle afflicted with bovine spongiform encephalopathy (BSE, or mad cow disease) and may rarely be transmissible by transfusion. These are the tests performed before transfusion to ensure that the donor's blood will not react adversely with that of the patient when it is transfused. The major crossmatch is performed, in which the patient's serum/plasma is mixed with the donor's red cells. For the blood of the donor to be considered compatible, there must be no reaction between the patient's serum/plasma and the donor's cells. This is a plasma component prepared from frozen fresh plasma by slow thawing of the plasma which causes precipitation of proteins. This precipitate will go back into solution if the temperature is not carefully controlled to remain sufficiently low. Cryoprecipitate is rich in factor VIII and fibrinogen. Crystalloids are aqueous (water-based) solutions of low molecular mass salts that may be used for rehydration. They are isotonic or slightly more hypotonic than blood and may contain dextrose. Although they are intravenous replacement fluids, they cross the capillary membrane from the bloodstream into the interstitial spaces and are rapidly distributed within the extracellular compartment. This is a bluish discolouration of the skin that is caused by poor oxygenation of the blood, or by a poor circulation. When an individual donates specifically for his/her cells (usually platelets but occasionally white cells or red cells) the process is termed cytapheresis. The remaining components are immediately re-infused. Sophisticated programmable blood separating machines that are linked to the donor, are used. In this way, many more cells than those available from a whole blood donation may be gathered from one donor. The process of obtaining platelets from apheresis is called plateletpheresis. Harvesting of white cells is called leucapheresis or granulocytapheresis, and collecting red cells is called erythrocytopheresis. These are anti-viral and anti-tumour agents produced by the body, as part of the system of immune defence. Cytokines (e.g. interleukins) are released into the blood by white cells and in transfused blood components can lead to immune modulation in the recipient. Cytomegalovirus (CMV) belongs to the herpes group of viruses and may be transmitted by blood transfusion (components that contain leucocytes). In immunocompromised CMV-negative patients, the transmission of CMV infection can be very serious, causing morbidity or mortality. Selected blood donations may be tested for anti-CMV, so that newborn infants or other immunodeficient patients receive only CMV-negative blood transfusions. Alternatively, pre-storage leucocyte filtration may be carried out on all or selected donations. As CMV is usually found within the white cells, filtering the blood, particularly prior to storage before white cells start to disintegrate, reduces the risk of transmission. Cytopenia is a lower than expected number of circulating blood cells of all types. A Dalton (Da) is the unit used in expressing the molecular weight of, for example, proteins. It is equal to 1/12 of the mass of one atom of carbon-12. DNA is the material found in the nucleus of cells that carries the genetic information. The chromosomes are made up largely of DNA. The diastolic blood pressure refers to the measurement taken when the heart is relaxed. Diastole refers to the short period of time when the heart is at rest and dilated between each contraction. Directed donations are those donated for a particular patient. It may be that the patient has been scheduled for elective surgery and will require blood. Friends or family members are recruited to donate blood, and this may be the result of the fact that the individual does not have confidence in the safety of the blood supply, or that there is not an adequate supply of blood from volunteer donors. In such cases, it has been found that directed donations are not as safe as voluntary donations, as friends and family coerced into giving blood are less likely to disclose risk factors. On the other hand, patients with antibodies to high incidence antigens may require directed donations from previously grouped individuals – who may be family members, or who have the same rare blood group as the individual requiring the blood transfu