A patient with suspected hemophilia has prolonged aPTT. A mixing study is performed by mixing the patient's plasma 1:1 with normal pooled plasma. The aPTT corrects immediately. What does this finding indicate?
- A Presence of a specific factor inhibitor
- B Presence of lupus anticoagulant
- C Factor deficiency without an inhibitor ✓
- D Contamination with heparin
Correct answer: C. Factor deficiency without an inhibitor
Explanation
Correction of aPTT on 1:1 mixing with normal plasma indicates a factor deficiency, because the normal plasma supplies the missing factor to reach 50% activity, which is sufficient to normalize the aPTT. A specific inhibitor (e.g., factor VIII antibody) or lupus anticoagulant would NOT correct the mixing study because they inhibit the added normal factors as well. Heparin contamination is detected by reptilein time or thrombin time.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.