In the following, we describe the clarification of a transfusion reaction after transfusion of a platelet concentrate to a 71-year-old female patient, further anamnesis unknown. The patient showed signs of a mild febrile transfusion reaction with a rise in body temperature from 37,7°C to 38,7°C. In this case, two different HLA laboratories were commissioned by mistake and two different results were obtained: HLA class I antibody positive and HLA class I antibody negative.

For clarification of transfusion incidents, we use the most sensitive method for antibody diagnostics, the LABScreen (One Lambda, CA, USA), to detect even weak antibodies that can be boosted during further transfusions and can lead to serious transfusion reactions (Müller, Markus M et al. 2015). Further differentiation and confirmation of a possible specific antibody was performed using the LABScreen Single Antigen HLA Class I (SA 1) test (One Lambda, CA, USA). Both assays were performed using serum according to manufacturer`s instructions. Investigations revealed that the second HLA laboratory involved used the Pak Lx (Werfen, BY, Germany). In order to rule out laboratory-related deviations, the sample was subsequently analysed in our laboratory also using the Pak Lx.

Although a specific antibody could already be suspected by the LABScreen due to distinct reactions of individual bead groups, the antibody specificity was confirmed in the SA 1 test for anti-HLA-B27 and the associated antigens of the Cregroup B7, B73, B60 and B61 with MFI values of over 1000 to 5000. Controversly, a re-test of the same blood sample with the Pak Lx also yielded a negative result for HLA class I antibodies in our lab.

Our case report illustrates that the most sensitive test for the detection of HLA antibodies should be selected, particularly for patients who receive increased platelet concentrates during the preparatory therapeutic phase. In a study by Reiher et al. (2017), the sensitivity of the HLA class I bead of the Pak Lx was compared with another test kit that uses several individual HLA antigen beads. The results indicate that the Pak Lx is less sensitive for the detection of HLA class I antibodies. Emerging false negative results and consequently incorrect therapeutic measures can lead to a boosting of subthreshold antibodies, causing adverse transfusion reactions.

There is no conflict of interest.