Problems highlighted when using anticoagulated samples in the standard tube low ionic strength antiglobulin test

Within the UK blood transfusion services, there is currently no recommendation for the use of either clotted or anticoagulated samples for antibody identification testing. This report describes three cases in which the detection of IgM antibodies was impeded by the use of anticoagulated samples. Two patient samples, referred for compatibility testing, were both identified as having IgM complement-activating anti-S and the remaining case involved an antenatal patient with IgM complement-activating anti-Vel. In all three cases, the coincidental referral and investigation of both clotted and anticoagulated samples led to the discrepancy in serum and plasma test results becoming apparent. Potential errors in selection of suitable blood for transfusion and appropriate antenatal management were avoided by correct identification of the antibodies present using the clotted samples.