A study of the errors produced when weak antibodies are tested by the indirect antiglobulin method

An investigation is reported into the error rate of the indirect antiglobulin test when random, weakly reactive samples are tested. Tests were completed by the majority of laboratory staff in 2 transfusion services and 3 major general hospital blood banks, during their routine daily work. A significant level of technical difficulty was revealed, from 5.2 to 60.8% of positive tests being called negative, and from 5.7 to 32.3% of negative tests being called positive. Reproducibility of weakly reacting duplicates was generally poor, as was the allocation of score values to the agglutination reactions. The significance of these findings relative to the content of quality control surveys is discussed.