Laboratory comparison of the VisuLize IX antigen assay with the Asserachrome IX antigen assay

Factor IX antigen levels are used primarily to assess factor IX levels in patients with liver insufficiency or who are receiving oral vitamin K antagonist therapy. We evaluated the test performance of a new factor IX antigen enzyme-linked immunoassay kit and compared it to our currently used enzyme-linked immunoassay method. Samples from normal donors and patients with known hemophilia B of varying severity were tested by using a predicate factor IX antigen method (Asserachachrome IX:Ag) and a new factor IX antigen method (VisuLize IX Antigen). The 2 methods were evaluated for performance, correlation, differences, and bias. Test samples included 46 normal donors, 14 commercial products, and 16, 18, and 15 severe, moderate, and mildly deficient factor IX deficient plasmas, respectively. The 2 methods correlated well using regression analysis. However, there were significant differences using the paired t test with bias plots indicating higher absolute values for the VisuLize IX antigen method in the severe and moderate deficiency range, but not the normal range. Testing commercially prepared survey material, the Asserachrome method demonstrated a consistently lower result than expected. The VisuLize factor IX is a new method for determining antigenic levels in human plasma. This method has a much shorter incubation time and demonstrates good correlation with current factor IX antigenic methods.