IMPROVED CHARACTERISTICS OF APC-RESISTANCE ASSAY - COATEST APC RESISTANCE BY PREDILUTION OF SAMPLES WITH FACTOR-V DEFICIENT PLASMA

Screening for a resistance against activated protein C(aPCR), which is in most cases caused by FV:Q(506) mutation, is performed by functiona l tests measuring the effect of aPC on activated partial thromboplasti n time (aPTT). Because of an insufficient discrimination between FV:Q( 506) mutation negative and positive individuals with the first generat ion of the functional test Contest aPC Resistance (Chromogenix AB, Mol ndal, Sweeden), the definition of an arbitrary cut-off level was only possible using the results of DNA :analysis. The use of an arbitrary c ut-off level still resulted in unsatisfactory low sensitivity and spec ificity for tile functional test. Thus, time- and cost-consuming DNA a nalyses had to be performed frequently to establish the diagnosis. Til e objective of this study was to evaluate an improved version of this assay that uses predilution of samples with factor V deficient plasma containing a heparin neutralizer. Using the data from 32 FV:Q(506) mut ation positive and 55 mutation negative individuals, the authors calcu lated a cut-off value resulting in an enhanced sensitivity (0.91 versu s 1.0) and specificity (0.77 versus 1.0) compared to the old one. Impr ecision was lowered from 5.36% (first generation) to 2.43%, in particu lar in samples with longer clotting times. In patients with prolonged aPTT, either caused by therapy with oral anticoagulants or heparin, co rrect results were obtained with the second generation assay, in contr ast to the first generation assay, With this second generation assay t he number of DNA analyses can be substantially reduced.