Detection of Factor VIII Inhibitors in Hemophilia A Patients

Factor VIII administration to hemophilia A patients results in an immune response (inhibitor formation) which significantly complicates the therapy. The present study was performed to determine the prevalence of inhibitor development in hemophilia A patients receiving recombinant factor VIII therapy. This was an observational descriptive study. Clotting factor inhibitor screening was performed by activated partial thromboplastin time mixing studies using normal pool plasma collected from twenty healthy donors. Bethesda assay for quantitation of factor VIII inhibitors was performed on samples which were positive with screening tests. Out of 229 patients with hemophilia A enrolled in the hemophilia society of Pakistan, Lahore center, 50 patients were selected. The mean factor VIII level in these patients was 2.46 +3.14. Out of 50 patients, 29 (58%) had severe hemophilia A (factor VIII level <1%), 17 (34%) had moderate hemophilia A (factor VIII level 1-5%) and 4 (12%) had mild hemophilia A (factor VIII level >5-30%). In this study, 12 patients (24%) were positive for inhibitors. Most of them 9 (75%) were low responders (<5 Bethesda units) with a mean Bethesda units of 1.82+0.473, while 3 (25%) patients were high responders (>5 Bethesda units) with a mean BU of 11.33+5.85. Patients were divided into two groups on the basis of the number of factor VIII concentrate therapies of <50 (group 1) times and >50 times (group 2). Inhibitor positivity was high (34.5%) in group I, as compared to group II (9.5%). Bleeding episodes were also more common in inhibitors positive patients. In this study, the inhibitor development in patients with hemophilia A receiving recombinant factor VIII concentrates therapy was 24% and the first fifty therapies were crucial for inhibitor development.