Resistance to activated protein C evaluated with APTT-based methods and DNA analysis

Summary Two approaches are at our disposal for the diagnosis of activated protein C (APC) resistance: 1) the semi-quantitative plasma test based on an aPTT assay and 2) the detection of the factor V gene defect by DNA analysis. In this work we evaluated sensitivity, specificity and diagnostic efficiency of the two plasma clotting tests at present available in Italy: Chromogenix and Behring, in 26 subjects found positive for Arg 506 →Gln mutation and in 44 healthy subjects negative for the mutation. A sensitivity of 100% was never achieved; The Chromogenix test choosing 1.88 as ration threshold (corresponding to the mean ratio-2SD), gave a specificity and a predictive positive value of 100%. The same accuracy indexes were achieved by the Behring test when a cut off of 1.43 (corresponding to the mean ratio-2SD) was used. Normalised ratios for both tests yielded similar results. Therefor both test can be used as pre-screening tests in the diagnosis of APC resistance but genotyping investigation is mandatory in the case of border line results.