USMLE-Rx Step 1 Qmax Challenge #1372

Check out today’s Step 1 Qmax Question Challenge.

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USMLE-Rx Step 1 Qmax Challenge #1372.pngA 10-year-old boy is brought to the emergency department after falling from his bicycle. He presents with a large, painfully swollen knee; aspiration shows gross hemarthrosis. On further questioning, the patient’s parents say that he bruises easily and that it took several days for the bleeding to completely stop after losing a tooth 1 month ago. His maternal uncle had similar bleeding difficulties. After further testing, the patient is diagnosed with an X-linked recessive disorder.

Which of the following laboratory test results corresponds to the patient’s disorder?

A. A
B. B
C. C
D. D
E. E


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12 replies »

  1. A)
    Hemophilia with Factor VIII (Antihaemophilic Factor) deficiency which is a component of Intrinsic Pathway of Coagulation which in turn is monitored by aPTT.
    It does not affect platelets, BT and Extrinsic Pathway of Coagulation.

  2. A, because bleeding time is normal in hemophilia (platelet function is intact), prothrombin time (PT) is normal in hemophilia (because of extrinsic factor, especially FVII, is normal in hemophilia – not in vitamin K deficiency or under warfarin treatment) and partial thromboplastin time (PTT) is extended since PTT involves all clotting factors (so including the ones involved in hemophilia) except FVII and FXIII.

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