A person with hemophilia can be diagnosed by factor assay, bleeding pattern, and family history (if any). A person with hemophilia A, B, and C has labs showing prolonged aPTT values and normal PT and TT values. In cases of mild hemophilia, the aPTT may only be slightly prolonged or even normal, especially if factors VIII and IX are still at 20% or more. A definitive diagnosis of hemophilia can be made by assessing the specific assay for the activity of factors VIII and IX.
