A 19-year-old man is brought to the hospital after injuring his knee playing football. The knee is swollen and painful to move. He has no prior history of bleeding disorders. Arthrocentesis of the knee reveals 20 cc of blood. Further investigations show that his platelets are 170,000/mL, PT is normal, PTT is elevated, bleeding time is normal, factor VIII is normal, factor IX is reduced, and the ristocetin cofactor assay is normal.For the above patient with a bleeding disorder, select the most likely diagnosis.
Haemophilia B is clinically indistinguishable from haemophilia A and is also inherited via the X chromosome. The bleeding time is usually normal, but the PTT is usually elevated. Differentiation from haemophilia A requires factor assay.
von Willebrand disease
hemophilia A
hemophilia B
thrombotic thrombocytopenic purpura (TTP)
Blood