A 29-year-old woman with two first-trimester pregnancy losses has activated partial thromboplastin time of 71 seconds (control 34) with a normal prothrombin time. A mixing study with pooled normal plasma fails to correct the aPTT. Platelet count is mildly reduced at 110,000/uL. Dilute Russell viper venom time is prolonged and confirmed on repeat testing. What best explains the isolated prolongation of aPTT in this patient?

• A Factor VIII inhibitor neutralising factor VIII in both patient and pooled plasma
• B Congenital deficiency of factor XII causing lifelong bleeding tendency
• C Antibodies against beta2-glycoprotein I interfering with phospholipid-dependent clotting assays in vitro ✓
• D Disseminated intravascular coagulation consuming factors II, V and VII

Explanation

Lupus anticoagulant is an IgG or IgM antibody directed against phospholipid-bound proteins, chiefly beta2-glycoprotein I. It binds the phospholipid used in aPTT and dRVVT reagents, prolonging these tests in vitro despite promoting thrombosis in vivo. It does not correct on mixing because the antibody persists. Factor VIII inhibitors also fail to correct but cause bleeding, not recurrent miscarriage, and DIC would prolong the PT and consume platelets far more severely.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.