Compatibility testing Article Swipe

The laboratory is a vital part of the transfusion chain, and successful pre-transfusion testing is dependent on staff in clinical areas providing timely requests for blood with adequate clinical details, accompanied by correctly labelled samples. The primary aim of pre-transfusion testing is to provide red cells that will have the maximum survival following the transfusion and/or blood components that most effectively improve haemostasis, without causing an adverse reaction in the patient. This requires correct identification of patients ‘vein to vein’ and provision of ABO compatible blood that is antigen negative for any clinically significant red cell antibodies present in the patient’s serum/plasma. A secondary aim is that blood selected for transfusion should not expose the patient to future risks, e.g. sensitisation to the D antigen in females with childbearing potential or the alloimmunisation of patients who, because of their medical condition, will require ongoing transfusion support. Although the principles of pre-transfusion testing are universal, practice will vary depending on resources available, such as availability of blood components (vs. whole blood), reagents (for ABO/D typing, crossmatching, antibody screening and antibody identification), information technology (IT) and automation, and staff with specialist transfusion training. Therefore, different strategies will be required to achieve the aims. A full understanding of the process is required to be able to design the best system possible in any given circumstances. It is advisable to identify the critical points and carry out a risk assessment, bearing in mind that misidentification of the patient or sample is a major risk and that effective procedures and policies can do as much to improve safety as accurate and sensitive testing. It is important to achieve a balance between providing blood components of the ideal specification and ensuring timely life-saving transfusions; this is a clinical decision made on a case by case basis by the medical team with input from the laboratory. All laboratory testing and processes should be subject to good laboratory practice and operate within a quality management system (see Section 16: Quality). Effective communication between all staff groups involved in the transfusion chain is essential to ensure patient safety. Practice in clinical areas such as appropriate prescribing, sample collection, administration of blood and monitoring of transfusions in progress can be influenced and improved by the establishment of a hospital transfusion committee. See Section 14: Transfusion risks and haemovigilance. Pre-transfusion compatibility testing in the laboratory must detect ABO/D incompatibility between the patient and donor that can cause serious and even fatal haemolytic transfusion reactions. This requires accurate ABO/D grouping of the patient and donor and an additional test (serological or electronic) to confirm ABO compatibility before blood is issued. The two most common causes of error in transfusion are misidentification of the patient, or the sample. This can happen either at the bedside when the sample is drawn from the wrong patient, or in the laboratory when the wrong sample is selected for testing. Studies have shown that mistakes are more likely to occur during emergency situations when personnel are working under extra pressure and time constraints. Systems to avoid patient misidentification are usually distinct and separate in clinical and laboratory areas. Therefore, good laboratory practice will not be able to prevent the consequences of patient misidentification at the bedside. Likewise, good bedside identification will not prevent identification errors in the laboratory. One of the important functions of a hospital transfusion committee is to address such issues. The role of the hospital transfusion committee is described in Section 14: Transfusion risks and haemovigilance. It is important that standard operating procedures (SOPs) are in place for all critical tasks related to the transfusion process. All personnel authorised to carry out these tasks should be trained and able to demonstrate competency. SOPs should stress the importance of checking and rechecking to ensure that patient and unit misidentification does not occur at any stage in the process. A system should be in place to link the patient to the correct case notes in the event of the patient being unconscious or unable to confirm their identity for any other reason. There should be no interruptions or distractions when taking the sample from the patient, recording the details on the label and request form, and checking for errors or omissions. If there is an interruption, the process of checking should be repeated and if there is any doubt, a fresh sample should be drawn. For manual compatibility testing, dry tubes are suitable for the collection of blood samples from patients. However, if any part of the testing is automated, anticoagulated samples are required. If a sample is anticoagulated with a substance that chelates calcium, such as EDTA, then complement-dependent antibodies will not be detected during crossmatching or antibody screening. The benefits of automation, in terms of standardisation and security of sample identification, outweigh the risk of failing to detect a complement dependent antibody. Whilst every sample received by the laboratory should be treated as potentially infectious and appropriate care taken during handling, samples from patients with haemorrhagic diseases such as Marburg fever or Ebola fever carry a greater risk, as the viruses responsible for these infections are very easily spread by blood and other body fluids. Samples from these patients should not be submitted to the laboratory, and arrangements should be made by the medical officer of the blood service, with the prescribing clinician, to use uncrossmatched Group O red cell concentrate for such patients. When several requests reach the laboratory at the same time, they should be handled and registered separately, one at a time. Each laboratory should have a policy for sample acceptance that is known to staff in the laboratory and clearly communicated to staff in clinical areas. If all patient demographics do not correspond, or if any information deemed necessary by local policy is missing, the request should not be accepted. The requesting clinician should be contacted immediately and asked to submit a new sample. The original sample should be discarded. The request form should include a clinical diagnosis and state the blood components required, the reason for the transfusion and the urgency of the request. If this information is not present, it should be obtained from the requesting clinician, as it may influence the laboratory’s decisions regarding the pre-transfusion tests required, priority of testing and specifications for components to be prepared. Provision should be made on the request form, for the clinician to provide information on a history of transfusion, so that laboratory records may be consulted to determine ABO/D blood type, whether irregular antibodies were detected, or whether there was an adverse reaction to a previous transfusion. All communication with clinical areas regarding patients should be clearly documented on the crossmatch request form, together with dates and times, by the blood bank technologist receiving the message. Any information regarding patients and their records is confidential and should not be divulged to anyone not in authority to receive it, which includes family members. On acceptance, every request should be assigned a unique laboratory number to identify the sample and the respective documentation. This number should appear on the sample tube, the request form and in the crossmatch register if a paper system is used. If a laboratory IT system is used, this number should be in the form of a barcode as well as an eye readable version. Numbering samples for processing in the laboratory is prone to transposition/transcription error and checks should be in place at every stage in the process to ensure that results are attributed to the correct patient. The patient and request details should be recorded, either in a laboratory IT system capable of recording and retrieving the information below, or in a paper crossmatch register, or in a combination of both. If the sample was taken into a dry tube, it should be fully clotted before use to avoid interference by fibrin in the tests. Requests may be received for issue for a specific number of red cell units to be crossmatched or for ‘type and screen’. The option of ‘type and screen’, is useful when it is not certain that the patient will need a transfusion, but it is only possible where there is access to reliable antibody screening. The attending clinician submits a sample and request form, with the understanding that blood will only be crossmatched if needed, usually over the next few days (or 72 h maximum if the patient has been recently transfused). During this time, blood may be ordered by telephone and can be provided more rapidly than usual as the sample is already checked for labelling and the patient has already been ABO/D typed and screened for irregular, clinically significant red cell antibodies. Determination of the ABO/D type of the patient before blood is needed provides time to resolve any potential grouping anomalies, check that group compatible units are available in stock and, if necessary, to arrange to obtain such units from another area. Antibody screening in advance allows time for a positive antibody screen to be investigated, atypical antibodies to be identified (or referred for investigation) and compatible blood to be sourced by screening donations for antigen negative blood. In this situation, it would be advisable to undertake the crossmatch as soon as suitable units are found, especially where reliable antibody identification cannot be guaranteed due to lack of resources. If a transfusion is subsequently required, delays due to unexpected incompatibility can then be avoided. The prescribing clinician should be notified at the outset of expected delays in the provision of compatible blood. It is useful to develop a Maximum Surgical Blood Ordering Schedule (MSBOS) negotiated with clinicians through the hospital transfusion committee, where either a ‘type and screen’ is performed (with blood available within an agreed timescale), or a set number of units are made available for a list of common surgical procedures. Where there is an effective MSBOS, most type and screen requests are not converted into crossmatches, reducing demand on the laboratory and preserving reagents and consumables. This system also prevents units of blood being reserved for cases where they will not be used, facilitating better stock control and reducing blood wastage. During a single transfusion episode, requests for additional units to be crossmatched for a patient are sometimes received by the blood bank. The same crossmatch sample may continue to be used, provided that there is sufficient sample remaining for the testing required. However, the sample used should not be more than 72 h old, since the first unit of blood was transfused, in this or any other recent episode of transfusion; in this situation, a fresh sample should be requested if additional units are required to be crossmatched, as it is possible that antibodies may have been produced in response to donations transfused, after the original specimen was taken. All crossmatch specimens drawn from patients should be stored for at least a week at 4 ± 2°C in case of an untoward reaction being reported from the clinical area, in which case the specimen must be available for transfusion reaction/investigative testing in the laboratory, to determine if possible, the cause of the reaction. Patient records are a vital resource in the process of pre-transfusion testing/checking and great care and consideration should be given to how they are created and maintained so that they are accurate, complete and easily accessible when required. If a laboratory IT system is used the patient can be electronically linked to previous records (laboratory results, donations issued, comments) to form a cumulative transfusion record that facilitates checking vs. previous laboratory results and transfusion history. Wherever possible information should be entered into IT systems in the form of ‘coded comments’ so that it is more easily searchable and retrievable. Secure systems should be in place to check that the patient’s first name, last name and date of birth match before linking electronic records or updating paper records. Patient and donor records are useful when it is necessary to trace the patient into whom a donation was transfused, so that in the event of a recall, e.g. where the donor is subsequently found to have a transfusion transmissible infection, action may be taken according to the policy of the blood service. Checking historical records can also help to prevent delayed transfusion reactions when antibodies found in the past are no longer detectable but have the potential to be boosted by another transfusion; to prevent this, antigen negative blood must be crossmatched in such a situation. Some clinically significant antibodies are often transient in nature, such as anti-Jka. When the record states that the patient has anti-Jka, Jk(a-) donations should be selected for the IAT crossmatch, even if the antibody is not detectable in the current sample. In a routine situation these tests are performed on patient samples for ‘type and screen’ and for crossmatching. This testing takes place as soon as possible after the samples are received and before the final check to confirm compatibility (usually a serological crossmatch). The reliability of results will depend on whether the testing is manual where the risk of procedural error is high or whether automation is used allowing standardisation of testing, electronic recognition of samples/reagents and secure transfer of data to IT systems. The use of previous groups in the testing algorithm will depend on the level of confidence in historical records. The protocol for repeating tests before issue and checking procedures at each stage should be designed to reflect these differences. ABO grouping is the most important element of pre-transfusion testing, since consequences of error can be fatal, and therefore, priority must be given to ensuring the sensitivity and security of the testing system. For all patient samples, testing should include a ‘forward’ (red cell) group using anti-A and anti-B reagents (monoclonal where possible, with an anti-B that does not detect acquired B antigens), and a ‘reverse’ group using A cells and B cells at a minimum. Before blood is issued a comparison must be made with a second group; if there is a reliable historical group on record, this can be used for this purpose. If there is no such previous group on record, a repeat group (minimum of cell group using anti-A and anti-B) is required before blood is issued. If testing manually, the repeat group should be performed if possible, by a second technologist without sight of the original result. For a repeat group, it is important to return to the original sample, and not to use an existing cell suspension or aliquot, otherwise any sampling error that may have occurred the first time will be replicated, and also the opportunity to re-check the sample identification will be missed. The prominence given to D typing will depend on the frequency of the D antigen in the population. However, it is especially important not to stimulate the production of immune anti-D in females with childbearing potential, since anti-D can cause severe haemolytic disease of the fetus and newborn (HDFN). Therefore, the reagents, test systems and controls used for patient pre-transfusion testing should be designed to minimise the risk of a false-positive result. Monoclonal saline reacting IgM anti-D reagents are recommended. It is not advisable to confirm D negative results using an anti-D reagent by IAT, or to use potentiated reagents without a suitable control reagent, as false-positive results can be obtained if patient red cells are DAT positive. Rh system reagents other than anti-D are not advised for pre-transfusion patient testing since these add no value to the testing, and problems can arise in interpretation. Neonates must be tested for ABO/D with a forward (cell) group. Reverse or serum/plasma grouping may not be useful as isohaemagglutinins are not usually developed at this stage. The ABO-D forward grouping should be repeated (going back to the original sample) if there is no historical group. A direct antiglobulin test (DAT) should also be performed on the neonate’s red cells. Where anomalous, i.e. irregular/atypical, results are obtained for ABO grouping and transfusion cannot be avoided, Group O red cell concentrate should be given until the patient’s group is confirmed. Where equivocal, i.e. uncertain, results are obtained for D typing, patients should be treated as D negative. If the patient has cold haemagglutinin disease (CHAD) with haemagglutinins reactive above 30°C, the sample may be auto-agglutinated on arrival at the laboratory. A free suspension of cells for ABO grouping can usually be obtained by washing the patient’s cells in saline warmed to 37°C. In severe cases, it may be necessary to obtain a sample from the patient and keep it at 37°C continuously until the serum/plasma and cells have been separated in the laboratory. The prescribing clinician should be informed of the presence of cold agglutinins in the patient, as it may be necessary to warm the blood when it is transfused, using a validated blood warmer specifically designed for that purpose. The laboratory will have to decide whether to use anti-IgG or broad spectrum AHG for IAT testing as part of antibody screening, identification and crossmatching. A broad spectrum AHG (anti-IgG and anti-C3d) will detect both IgG and complement bound on the red cells, but only in samples that have been taken into a dry tube, so this is not an advantage if EDTA tubes are used to facilitate automation. Use of anti-IgG AHG avoids numerous false positives/cold/apparent non-specific antibodies, especially when testing with polyethylene glycol (PEG). In a laboratory where antibody screening is not available, pre-transfusion testing proceeds immediately to the serological crossmatch. Where reagent screening cells are available, an IAT antibody screen should be performed on all patients with requests for blood and/or type and screen, and on mothers of neonates (usually applies to infants <4 months of age) requiring transfusion. Excluding emergencies, this should always take place before blood is issued. The antibody screen is more sensitive than the crossmatch in detecting antibodies since the cells are selected for apparent homozygous expression and are kept in conditions that will better preserve red cell antigens. The screen may detect weak antibodies that could be missed by the crossmatch alone. The aim is to detect only clinically significant antibodies, and where the IAT is sensitive and reliable there is no need to screen by other methods, such as using enzyme treated cells. Screening cells should be Group O and have expression of antigens to which clinically significant antibodies can be formed, i.e. and Screening cells should be selected to reflect the antigen frequency of the population. In of the where there is a high of clinically significant antibodies to other antigens e.g. then cells these antigens should be cells from different donations should not be and cells with homozygous expression of antigens antibodies are clinically significant and should be i.e. and The reagent screening cells should also lack frequency antigens where the antibodies are not of clinical e.g. If an antibody is detected it should be identified (or referred for to crossmatching If antibody identification is not able to be it may be possible to the number of possible of the antibody using the antigen of the screening cells. testing the screening cells the patient serum/plasma by other than IAT that do not require additional can help with For testing by direct at may help to or confirm antibody such as and a this may information on clinical and of the antibodies detected (see and can also an of the of compatible blood by crossmatching If all the screening cells are positive by IAT, it is useful to set an by IAT, i.e. patient serum/plasma vs. patient cells to the of an (see Antibody identification antibody identification can be set by IAT and it is advisable to include an test serum/plasma vs. patient red as this will whether an is A process for and of the common antibody should be additional and may be used to with this, as by the results of the The reactions obtained with the screening cells should also be taken into consideration when antibody identification results, and the patient’s if of the antibody present will to the clinical from the that antibody cause haemolytic transfusion reactions e.g. most Rh antibodies, is For other the is not as e.g. and may depend on the from ABO antibodies, above are clinically are useful to determine the but should be used with where antibody have not been fully as weak of common clinically significant antibodies, e.g. and/or but significant antibodies with at e.g. could be Antibody identification is not always and in the antibody screen and identification is one of the most problems to resolve when providing blood for transfusion. In this situation the patient’s medical the history of previous transfusions and the results of serological testing, should always be Some of the more common causes of are as If the patient is known to from an or in the of a previous where warm reacting are detected and the DAT is it can be that all blood crossmatched will be by A should be made for or to determine whether the patient’s are any clinically significant If the patient’s Rh is known or the patient’s red cells can be typed using saline reagents, it is to Rh blood. Where there is by IAT but the DAT and are the is that the reactions are due to an antibody to a high antigen or to a of more common antibody The of and the by which the were detected are significant in a case However, identification is as is of other antibody that may be and it is likely that will be required to resolve these that are negative for a combination of antigens may be to and it may be necessary to obtain blood from a donor where blood donations from with antigen negative blood may be stored are and stored using at for a This process takes time and the is (see Section Blood processing for more Some IAT antibodies, non-specific for blood group can be such as where the is to IAT using a saline of antibodies that may be and their clinical in terms of to cause The also whether antigen negative blood must be selected for IAT crossmatch or whether compatibility can be by a negative reaction in the IAT crossmatch alone. a donations that are to their date should be used It is standard practice to use stock blood in date for routine transfusion requests so that there is of blood date and to be discarded. In where there are in sufficient stock control is more When blood for crossmatch, consideration should be given to the patient’s clinical condition, the urgency of the request and the potential risk to the patient of alloimmunisation on future and/or The final of every donation that through the laboratory should be i.e. transfused, or for another reason. The laboratory should have an in place with clinical areas to ensure that the final of each donation is so that the crossmatch register, or IT stock control can be to record that the blood or was to the patient for whom it was issued. Blood selected for crossmatch should be ABO blood type or if this is not available, group For a Group A patient should be given Group A blood. If Group A blood is not available, then Group O red cells could be selected cell will very anti-A or but with whole blood there is a risk of the anti-A and/or anti-B and donations tested and found negative for high anti-A and anti-B should be selected to avoid haemolytic reactions in with the ABO antigens. should also be given to this risk even when red cell if the patient is especially e.g. a (see Section testing for more If a patient is Group and Group donor blood is not available, then Group A or B blood may be selected depending on which is more available usually on the frequency of the blood group in the donor type as very weak of A should receive Group O blood. type with a very weak A antigen should receive Group B blood. where group blood is not available or where stock management requires use of ABO units to prevent blood wastage. ABO compatible for the transfusion of red cells, or into of the different ABO blood D negative donations are often in and possible, should be for D negative D positive should not be given D negative blood there are such as emergency transfusion or where the D negative are to and will be otherwise D negative should be given D negative blood possible, with priority given to patients with immune should be with D positive in to avoid transfusion and to females with childbearing potential all females to avoid of immune anti-D that could cause in future If necessary, D positive blood can be given to other D negative but this must be in their patient records to the laboratory of the potential for immune anti-D in such if transfusion is required in D positive blood be given to D negative females of childbearing potential, as a life-saving last the attending clinician should take for the decision to do In this situation, or where D positive blood was in anti-D should be given immediately to prevent of immune anti-D in such Where whole blood is to be transfused, donations tested and found negative for high anti-A and anti-B should be selected for ABO to avoid haemolytic reactions in with the ABO antigens. (see Section testing for more that is ABO is rapidly in the of the and anti-A and/or anti-B may also be by antigens present on a so is to cause a serious reaction. This may not be the case following