Physiology & Biochemistry · patient case question
Her brother has hemophilia A. Which laboratory test is characteristically abnormal in that condition?
Patient case: Family History and a Preoperative Workup
Patient: 26-year-old female
Chief Complaint: “My wisdom teeth need to come out and I want to make sure everything is safe first.”
Background: Multiple sclerosis diagnosed 2 years ago, currently in remission. Total thyroidectomy 6 months ago for papillary thyroid carcinoma, with persistent hoarseness since surgery. Her mother is a known carrier of Duchenne muscular dystrophy. Her brother has hemophilia A. She is planning a pregnancy within the next year.
Medications: Levothyroxine · Glatiramer acetate
Vital Signs: BP 114/70 mmHg · HR 76 bpm · RR 16 · T 98.4°F
Findings: Persistently breathy, hoarse voice. Well-healed anterior neck incision. Four impacted third molars planned for removal. Ibuprofen is planned for postoperative analgesia.
Show answer and explanation
Correct answer: C. Activated partial thromboplastin time
- A. Incorrect. Prothrombin time assesses the extrinsic pathway — factor VII — and is normal in hemophilia A. It is used to monitor warfarin and to assess hepatic synthetic function.
- B. Incorrect. Bleeding time reflects platelet function and vascular integrity. It is prolonged in von Willebrand disease and thrombocytopenia, but is normal in hemophilia A since platelets are unaffected.
- C. Correct. Hemophilia A is a deficiency of factor VIII, a component of the intrinsic pathway, which the activated partial thromboplastin time measures. It is prolonged, while prothrombin time, bleeding time, and platelet count all remain normal.
- D. Incorrect. Platelet count is normal. Hemophilia is a coagulation factor deficiency, not a platelet disorder.
Note: A clean way to remember it: PT and the extrinsic pathway go with warfarin; PTT and the intrinsic pathway go with heparin and with hemophilia. Both hemophilia A (factor VIII) and hemophilia B (factor IX) prolong the PTT.
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