[Effect of HLA antibodies on the gel centrifugation test]

We studied 39 samples of patients showing unexplainable but reproducibly positive indirect antiglobulin test (IAT) in the gel centrifugation (ID Micro Typing System, DiaMed) and negative auto-control test. Additionally 30 sera with defined red cell antibodies (control group) were tested. In 87.2% HLA antibodies could be found (none in the control group). After platelet absorption, 83.9% of the sera became negative in IAT. When IAT, microlymphocytotoxicity test (MLT) and platelet adhesion fluorescence antiglobulin test (PAFT) were performed with the cells of the same donors in parallel (n = 30) the IAT only became positive with the cells of donors (n = 21 = 70%) who also reacted in the MLT and/or PAFT. The tube test mostly was negative. The immunoglobulin class always was IgG. The specificity of the responsible HLA antibodies could be identified in 13 samples and was anti-HLA-B7, -B17, -A2, -A28 and mixed antibodies of these specificities. We conclude that unexplainable positive reactions in the IAT with gel centrifugation mainly are derived from HLA antibodies of high concentration which obviously play a greater role in the gel centrifugation than in other test methods. In cases of such unexplainable positive reactions the routine use of pooled platelets for absorption is recommended. In addition, test cells for antibody screening and identification by gel centrifugation should be typed at least for Bga (HLA-B7) in order to more easily recognize these irrelevant antibodies.