Evaluation of a highly specific functional test for the detection of factor V Leiden.
In the present study, a new functional test for the detection of increased resistance of coagulation factor V to degradation by activated protein C (factor V Leiden mutation) was evaluated. The STA-STACLOT APC-R Test (Diagnostica Stago, Asnieres, France) is based on the specific activation of factor X by Crotalus viridis helleri snake venom. The results are given as clotting time in seconds of the patient's plasma in the presence of venom and activated protein C. The intra-assay coefficient of variation was 2.17% (n=20) for samples within the normal range, and 1.70% and 1.42% (n=20) for the plasma of a heterozygous or a homozygous carrier of the factor V Leiden mutation, respectively. The inter-assay coefficient of variation (n=10) was 7.75% for the plasma of a healthy donor, 5.05% for the plasma of a heterozygous carrier and 3.38% for the plasma of a homozygous individual. The normal range (5th-95th percentile) of 136.4 s-174.7 s was derived from the clotting time of the plasma of 38 healthy controls. Values below 136 s were found in every sample from patients carrying the factor V Leiden mutation (n=52), whereas no patient with protein C (n=11) or protein S deficiency (n=10) had reduced clotting times. Homozygous carriers of the factor V Leiden mutation had clotting times shorter than 66.0 s and heterozygous carriers had clotting times longer than 80.0 s. Thus, based upon the individual clotting time, patients homozygous for factor V Leiden mutation could easily be distinguished from normals or heterozygous individuals. The influence of coagulation factor X, V, or II deficiency on the STACLOT APC-R Test was evaluated and revealed prolonged clotting times at factor V activities below 50%. In the presence of lupus anticoagulant the specificity of the STA-STACLOT APC-R Test was clearly decreased. In the present study, we clearly show that the STA-STACLOT APC-R Test is able to discriminate carriers of the factor V Leiden mutation from healthy controls or patients with protein C or protein S deficiency.
Quenhenberger
P
P
Department of Medical and Chemical Laboratory Diagnostics, University of Vienna, Austria.
Handler
S
S
Mannhalter
C
C
Pabinger-Fasching
I
I
Speiser
W
W
D000328:Adult; D001777:Blood Coagulation; D001780:Blood Coagulation Tests; D003435:Crotalid Venoms / Q000378:metabolism; D005165:Factor V / Q000032:analysis* / Q000235:genetics; D005170:Factor X / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D017354:Point Mutation; D011486:Protein C / Q000378:metabolism; D020151:Protein C Deficiency / Q000097:blood; D018455:Protein S Deficiency / Q000097:blood; D012016:Reference Values; D012680:Sensitivity and Specificity; D013997:Time Factors
D003435:Crotalid Venoms; D011486:Protein C; C095381:factor V Leiden; D005165:Factor V; D005170:Factor X