What is the diagnostic test for hemophilia a?

Factor VIII level. Hemophilia a results from the relative deficiency of factor viii coagulation protein. There are several degrees of severity depending upon the residual fviii levels. Diagnostic test is to measure the fviii level and exclude any possible inhibitors of the test measurement.
Hemophilia. In patients presenting with a bleeding diathesis of unknown cause, diagnosis of one of the hemophilias is made via a family history (particularly of the mother's side of the family), screening tests (starting with platelet count, prothrombin time, and activated partial thromboplastin time), and specific assays.