Quantification of human platelet antigen-1a antibodies with the monoclonal antibody immobilization of platelet antigens procedure

BACKGROUND: Fetal-neonatal alloimmune thrombocytopenia results from a maternal alloimmunization against fetal platelet (PLT) antigens. In Caucasian persons, human PLT antigen-1a (HPA-1a) is the most frequently implicated antigen. Our aim was to develop a method supported by a mathematical approach to quantify HPA-1a antibodies. STUDY DESIGN AND METHODS: The monoclonal antibody immobilization of PLT antigens (MAIPA) protocol was applied on serial dilutions of a serum with high concentration of HPA-1a antibodies used as reference. Two mathematical procedures were used: the standard curve was constructed with a linear and a logistic regression. These regressions were used to calculate the amount of antibody in 14 test serum samples from mothers with detectable anti-HPA-1a. RESULTS: Similar quantifications were obtained with both mathematical procedures. In 11 serum samples, the results, expressed in arbitrary units (AU), ranged from 62 +/- 4 to 1096 +/- 19 with the linear regression and from 62 +/- 4 to 1117 +/- 38 with the logistic regression. In addition, the linear regression allowed us to measure 3 test serum samples with low antibody concentrations from 4 +/- 2 to 44 +/- 3 AU, whereas the logistic regression was not suitable for the quantification of antibodies in these serum samples. CONCLUSION: A simple quantification method was developed for anti-HPA-1a, based on the MAIPA procedure, allowing further studies concerning correlations between anti-HPA-1a quantification and clinical relevance.