The Use of Chromogenic Factor VIII Assay Changes Treatment Approach in a Portion of Mild Hemophilia A Patients with Factor VIII Assay Discrepancy

Introduction Hemophilia A is an X-linked inherited bleeding disorder characterized by a deficiency of coagulation factor VIII (FVIII). FVIII assays used for diagnosis and classification of hemophilia are the widely used one-stage assay (OSA) and the chromogenic assay (CSA), a more costly and less commonly used test. The CSA has the advantages of improved precision and insensitivity to pre-activation effects of FVIII that can lead to erroneous results. In approximately one-third of mild hemophilia A cases, reliance on OSA can lead to overestimation of factor level in comparison to CSA, and this ‘discrepancy’ phenomenon is closely associated with the FVIII molecular abnormality. In mild or moderate hemophilia A, assay discrepancy can lead to misclassification or inappropriate treatment. The objectives of this retrospective study were to determine the proportion of patients with OSA/CSA discrepancies defined by OSA to CSA ratio of >1.5 or 18 years old) patients with mild or moderate hemophilia A followed at the Adult British Columbia Hemophilia clinic with concomitant OSA and CSA results between January 2013 and March 2019. Data collected included patient age, disease severity classification, baseline OSA FVIII:C, and F8 gene mutation. Bleeding phenotype and impact of discrepancy on treatment approach was evaluated and determined independently by two individuals and was correlated with concomitant OSA and CSA. Gene mutation data was collected to determine whether OSA/CSA discrepancy has been previously reported in the international hemophilia A mutation database (www.factorviii-db.org). Descriptive data was reported as medians and ranges. Statistical analyses using Spearman's correlation, logistic regression and receiver operating characteristics (ROC) curve were performed using IBM SPSS v. 22.0. Results 98 patients were included in the study with median age of 53 years (18-88). 75 patients were classified by OSA at baseline as mild and 23 patients as moderate severity. Median FVIII:C by OSA was 15% (6%-40%) in the mild group and 3% (1%-5%) in the moderate severity group. Median F