A SIMPLE PROCEDURE THAT INCREASES THE SPECIFICITY OF THE ACTIVATED PROTEIN-C RESISTANCE TEST IN SAMPLES CONTAINING ANTIPHOSPHOLIPID ANTIBODIES

It is well known that plasmas with lupus anticoagulants (LA) may give false low activated protein C (APC) ratios, and these false positive t ests are not necessarily corrected by mixing with factor V deficient p lasma (FVdef). In the present study, we show that repeating the test a fter mixing 1+1 with pooled normal plasma (NP) instead of mixing with FVdef confirm the presence of the Leiden mutation (FV-Leiden) in patie nts with antiphospholipid antibodies (APA). Samples from sixteen patie nts with a low APC-ratio were examined. Eight samples contained APAs, including five samples with LA. Results: The APC-ratios of eleven samp les, including four with APAs, became normal when retested after mixin g the plasma 1+1 with NP. All of them were heterozygous for FV-Leiden. One additional patient, who had partial correction of the APC-ratio, proved to be homozygous for the Leiden mutation. The remaining four sa mples, ail of which had high positive tests for APAs, remained unchang ed. One of these four was heterozygous for FV-Leiden, while the other three had normal FV. Conclusion: Normalisation of a low APC-ratio afte r dilution 1+1 with NP confirms the diagnosis of FV-Leiden. PCR analys is could be reserved for cases not affected by this procedure. (C) 199 7 Elsevier Science Ltd.