Rapid anti-HPA-1a antibody quantification with a Luminex bead-based assay: A method evaluation

High concentration of human platelet antigen-1a (HPA-1a) antibodies is reported to be associated with severe foetal and neonatal alloimmune thrombocytopaenia (FNAIT). The gold standard for quantification of anti-HPA-1a antibodies is the monoclonal antibody immobilization of platelet antigen (MAIPA) assay, which is a laborious method performed in only a few reference laboratories. The aim of this study was to evaluate the performance of the commercially available bead-based Luminex assay PakLx (Immucor) for quantitative measurement of anti-HPA-1a antibodies.

We analysed anti-HPA-1a antibody levels in plasma samples from 42 HPA-1a-negative women who had given birth to a child with thrombocytopaenia. Quantification of antibodies was performed with two different techniques: MAIPA analysed by spectrophotometry with results expressed in international units (IU)/mL, and PakLx analysed in the Luminex assay with results expressed as the mean fluorescence intensity (MFI).

In the comparison of the two methods' ability to stratify a result as either positive or negative, PakLx demonstrated 97.6% agreement with the MAIPA assay, with positive and negative predictive values of 96.7% and 100%, respectively. The correlation of the MFI values from PakLx with IU/mL in MAIPA assay was high, with a correlation coefficient (R²) of 0.92. MFI values were converted into semi-quantitative results: high, intermediate and low levels of anti-HPA-1a.

PakLx shows high agreement with the MAIPA assay and allows fast laboratory turnaround time for the determination of anti-HPA-1a antibody levels. The result may be of predictive value in clinical assessments.