engleski

Improvement of Staclot-APCr test for the detection of Factor V Leiden by using APCR ratio

The goal of every coagulation laboratory is to find a reliable screening test for the detection of activated protein C resistance (APCR) that will be suitable for routine work and that will at the same time reduce the need for genetic testing of Factor V Leiden (FVL). In the original STA– STACLOT APC-R Test (Diagnostika Stago, Asniè ; res, France) samples are analyzed only in the presence of APC and results are expressed as clotting times in seconds. The objectives of our study were to: 1. modify the original method by testing the samples simultaneously with and without APC, 2. adapt the modified test for the BCT (Dade Behring) coagulation analyzer, 3. find out if expression of results as APCR ratios can better discriminate FVL carriers from non-carriers. We tested 353 plasma samples from patients who were referred to our laboratory for thrombophilia screening and compared with DNA analysis for FVL. Among them, we analyzed plasma samples from 171 pregnant women, patients with protein C levels 12.4%-218.5%, protein S levels 7.1%-193.9% and FVIII:C levels 96%-580%. By DNA analysis, we identified 47 carriers of FVL (42 heterozygotes of whom 7 patients were receiving OAT, 5 homozygotes) and 306 non-carriers of whom 11 patients were receiving OAT (INR range: 1.36-4.66) and 15 were lupus anticoagulant positive (5 patients on OAT). Using a cut-off value of 1.81 for APCR ratio, the method provided 100% sensitivity and 100% specificity, as compared to 95.2% sensitivity and 97.2% specificity when results were expressed as clotting times of the original method (cut-off value: 113.8 seconds). There was no overlap between heterozygotes and normal subjects when results were expressed as APCR ratios (compared to 2 false positive and 8 false negative results with the original method) and no interference of known factors that affected the performance of APCR test.

APC resistance; FV Leiden

nije evidentirano