Which laboratory test is used to diagnose hemophilia (Factors VIII or IX deficiency)?

Hemophilia A (Factor VIII deficiency) and Hemophilia B (Factor IX deficiency) both affect the intrinsic coagulation pathway. The activated partial thromboplastin time (aPTT) tests the integrity of the intrinsic pathway (Factors XII, XI, IX, VIII) and the common pathway (Factors X, V, II, I). An elevated aPTT with normal PT (which tests the extrinsic pathway via Factor VII) is characteristic of hemophilia. Specific factor assays (Factor VIII or IX activity levels) confirm the diagnosis and quantify severity. Prothrombin time (PT/INR) is elevated in Factor VII deficiency and with warfarin therapy. In dental practice, hemophilic patients requiring invasive procedures should be managed in consultation with a hematologist, with Factor replacement therapy as needed.