🩺 MEDLAB BOT AI • CLINICAL MLS MCQ
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📚 Specialty: Hematology & Clinical Microscopy (#HematologyampClinicalMicroscopy)
🎯 Difficulty: Intermediate
🔢 Item: #Q8
❓ QUESTION:
A 68-year-old female with rheumatoid arthritis develops spontaneous, extensive subcutaneous hematomas. Coagulation testing reveals a normal PT of 12.0 seconds and an isolated prolonged APTT of 68 seconds. A 1:1 mixing study with normal pooled plasma yields an APTT of 31 seconds immediately upon mixing, but after incubating at 37°C for 2 hours, the APTT prolongs to 62 seconds. Which autoantibody is most likely responsible for these findings?
A) Factor VIII inhibitor
B) Lupus anticoagulant
C) Factor IX inhibitor
D) Factor XII inhibitor
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✅ CORRECT ANSWER: Option A
💡 CLINICAL RATIONALE & DIAGNOSTIC PEARLS:
Acquired Factor VIII inhibitors (neutralizing autoantibodies) characteristically exhibit time- and temperature-dependent kinetics. An initial 1:1 mix may appear corrected, but prolonged incubation at 37°C allows the antibody to progressively neutralize Factor VIII, re-prolonging the APTT. Lupus anticoagulants typically inhibit clotting immediately without requiring prolonged incubation, and factor deficiencies correct immediately and remain corrected after incubation.
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📢 MedLab Bot AI • Official Clinical Series
━━━━━━━━━━━━━━━━━━━━━━━━━━
📚 Specialty: Hematology & Clinical Microscopy (#HematologyampClinicalMicroscopy)
🎯 Difficulty: Intermediate
🔢 Item: #Q8
❓ QUESTION:
A 68-year-old female with rheumatoid arthritis develops spontaneous, extensive subcutaneous hematomas. Coagulation testing reveals a normal PT of 12.0 seconds and an isolated prolonged APTT of 68 seconds. A 1:1 mixing study with normal pooled plasma yields an APTT of 31 seconds immediately upon mixing, but after incubating at 37°C for 2 hours, the APTT prolongs to 62 seconds. Which autoantibody is most likely responsible for these findings?
A) Factor VIII inhibitor
B) Lupus anticoagulant
C) Factor IX inhibitor
D) Factor XII inhibitor
━━━━━━━━━━━━━━━━━━━━━━━━━━
✅ CORRECT ANSWER: Option A
💡 CLINICAL RATIONALE & DIAGNOSTIC PEARLS:
Acquired Factor VIII inhibitors (neutralizing autoantibodies) characteristically exhibit time- and temperature-dependent kinetics. An initial 1:1 mix may appear corrected, but prolonged incubation at 37°C allows the antibody to progressively neutralize Factor VIII, re-prolonging the APTT. Lupus anticoagulants typically inhibit clotting immediately without requiring prolonged incubation, and factor deficiencies correct immediately and remain corrected after incubation.
━━━━━━━━━━━━━━━━━━━━━━━━━━
📢 MedLab Bot AI • Official Clinical Series