Comparative analysis of chromogenic vs clot.based one stage APTT assay for determination of factor VIII level.

BACKGROUND: In the laboratory, factor VIII can be measured by three different methodologies, such as one-stage clotting assay, two-stage clotting assay, and chromogenic assay. These assays differ in ease of use, variety of reagents available, sensitivity to mild hemophilia A, and interference from lupus anticoagulants (LACs). Certain factor VIII gene mutations can cause discrepancy in results between one-stage activated partial thromboplastin time (APTT) and chromogenic assays. MATERIALS AND METHODS: The coagulometer for factor VIII assay is Sysmex CS-5100. All data were expressed as mean ± standard deviation (SD). RESULTS: A total of 135 cases were studied. Of these, 100 cases were of mild hemophilia A diagnosed by molecular genetics and, 15 cases were positive for LAC, which were confirmed by dilute Russell Viper venom test. Clot-based one-stage APTT assay showed 65% sensitivity and 80% specificity in diagnosing mild hemophilia A cases and out of 15 LAC cases, it showed false positivity in five cases. Chromogenic assay showed 85% sensitivity and 90% specificity in diagnosing mild hemophilia cases and was 100% specific in excluding LAC cases. CONCLUSIONS: One-stage APTT assay is the most commonly used test for determining factor VIII levels but chromogenic assay are considered as the gold standard and recommended as the reference method by European Pharmacopoeia and ISTH subcommittee. Mild hemophilia A patients with missense mutations show discrepancy between the one-stage clot-based APTT assay and chromogenic assays for determination of factor VIII level and this can lead to misdiagnosis or misclassification of mild hemophilia A. Therefore, it is recommended that both the assays should be used in the evaluation of mild hemophilia cases.

Comparative analysis of "APTT vs RVVT" based activated protein C resistance assay in the diagnosis of Factor V Leiden mutation.

BACKGROUND: Thrombophilia is a hypercoagulable state characterized by increased venous thrombosis. The most common cause of heritable thrombophilia is Factor V Leiden (FVR506Q) homozygous state, with a relative risk of 10-80 times as compared to normal individuals and Lupus anticoagulant is the most common cause of acquired thrombophilia. The main objective of this study is to compare the sensitivity of activated partial thromboplastin time (APTT) vs dilute Russell viper venom test (DRVVT) based APCR assays with predilution in Factor V-deficient plasma for diagnosis of Factor V Leiden mutation. MATERIALS AND METHODS: The coagulometer used for APCR test was Sysmex CS-5100. APTT reagent used is Pathrombin SL supplied by Siemens. All data were expressed as mean ± SD. Statistical analysis was done using unpaired students t-test and a P value <0.05 was considered as statistical significance. RESULTS: A total of 300 cases of APCR (200 cases of Factor V Leiden mutation was confirmed by PCR and 100 acquired) were studied. The sensitivity of screening APTT-based APCR for detection of Factor V Leiden mutation is 67% and for the noncarrier state, it is 62%. The sensitivity of modified APTT and DRVVT with predilution in FV-deficient plasma for detection of Factor V Leiden mutation is 82% and 84%, respectively and for acquired causes, it is 48% and 86%, respectively. CONCLUSION: Screening APTT test has increased in activated protein C resistance (APCR) due to Factor V Leiden mutation as well as acquired causes such as patients on direct-acting oral anticoagulants, warfarin, lupus anticoagulants, and oral contraceptive pills which are independent risk factors of venous thrombosis. Modified DRVVT with predilution in FV-deficient plasma is more sensitive than screening and modified APTT-based APCR test in the diagnosis of Factor V Leiden mutation and the former test can distinguish homozygous and heterozygous states from normal individuals.