Role of anti-prothrombin in antiphospholipid syndrome

We studied 99 patients with systemic autoimmune disease (5 males, 94 women; mean age 37 year, range 16-72): 28 Primary Antiphospholipid Syndrome, 67 Systemic lupus Erythematosus, 1 Mixed Connective Tissue Disease, 2 Undifferentiated Connective Tissue Disease and 1 Discoid Lupus. Based on the observation that native PT shows conformational changes in presence of Ca++ ions and discloses new epitopes available for binding with phospholipids, we performed 3 different methods for the detection of aPT in presence and absence of Ca++, finding a different incidence of specific autoantibodies, associated with clinical features of APS (aPT in presence of Ca++) or non associated (aPT in absence of Ca++). The presence of aPT was significantly associated also with the presence of Lupus Anticoagulant (LAC). The detection of aPT (in presence of Ca++) significantly enhances diagnostic sensibility of APS allowing the identification of a subset of patients (6/99) with clinical features of APS, but with negative LAC, aCL and aβ2-GPI; in fact (limited to thrombotic episodes) the sensibility rises from 56.2% with one test (LAC) to 81.1% with the application of LAC, aCL, aβ2GPI and aPT.