Refinement of the cutoff values of the HemosIL AcuStar assay for the detection of anticardiolipin and anti-beta₂ glycoprotein-1 antibodies

Background: The HemosIL AcuStar antiphospholipid assay (Instrumentation Laboratory, Bedford, MA, USA) is a fully automated assay using chemiluminescent technology for the detection of anticardiolipin and anti-beta(2) glycoprotein-1 antibodies. This assay showed excellent agreement between results of different laboratories. The cutoff values to define positivity were calculated in 250 healthy blood bank donors but were associated with large confidence intervals (CIs). Objective: The objective of this study was to more precisely determine the cutoff values of the HemosIL AcuStar antiphospholipid assay by increasing the number of healthy blood bank donors through a multicenter study and by applying a normalization procedure of the distribution of each antibody. Methods: Five laboratories participated to this study, allowing the inclusion of 626 samples. We used a Box-Cox power transformation method to normalize the distribution and calculate the 99th percentile and the corresponding 95%CI for each antibody. Results: The revised cutoff values were overall lower than those initially calculated with more stringent CIs and yielded a 4.2% increase in sensitivity with a 2.7% decrease in specificity regarding thrombotic events or obstetric complications. Conclusions: We provide refined cutoff values for the detection of anticardiolipin and anti-beta(2) glycoprotein-1 antibodies with the HemosIL AcuStar Antiphospholipid assay that should be preferred for routine use