Assessment of activated protein C resistance using a new and rapid venom-based test: STA Staclot APC-R.

Activated protein C (APC) resistance is related to a single point mutation in the factor V gene (FV:Q506) and appears to be the most common inherited risk factor for venous thromboembolism. A reliable screening test is therefore useful. We aimed to evaluate a new APC resistance test, on the basis of the procoagulant activity present in one snake venom of a crotalidae family: STA Staclot APC-R. We studied 36 consecutive patients with an acute deep venous thrombosis (DVT) confirmed by compression ultrasonography and carrying the FV:Q506 allele, assessed by DNA analysis, 103 of their family members and 35 consecutive patients with a proven DVT but who did not carry the FV:Q506 allele. Blood samples were collected within 24 h of admission for the DVT cases and on the day of medical registration for the family members. Tests were performed blind. The STA Staclot APC-R test, using a cut-off value of 0.80, had an overall sensitivity of 100% (95% CI, 95-100) and a specificity of 98.8% (95% CI, 92.0-99.6). An acute thrombosis process did not influence the performance of the test. We conclude that this test is easy and rapid to perform in every day practice and fulfills the criteria for a screening test.

Decision analysis model of prolonged oral anticoagulant treatment in factor V Leiden carriers with first episode of deep vein thrombosis.

OBJECTIVE: To assess the risks and benefits of oral anticoagulant treatment extended beyond 3 months after a first episode of deep vein thrombosis in patients who carry factor V Leiden mutation. Such patients have over twice the risk of recurrence after the recommended treatment period, but more information is required before widespread genetic screening can be recommended. DESIGN: A decision analysis Markov model (with data extracted form literature) representing the risks of developing symptomatic venous thromboembolism, the risks of major bleeding, and the efficacy of anticoagulant treatment. SUBJECTS: A hypothetical cohort of 1000 carriers of factor V Leiden recovering from a first episode of deep vein thrombosis in the lower limbs. MAIN OUTCOME MEASURES: Risks and benefits of, firstly, stopping oral anticoagulation 3 months after first episode of thrombosis with reinitiation of treatment only after recurrent thrombosis and, secondly, extension of oral anticoagulation up to 1 to 5 years. RESULTS: Despite consistent biases in favour of extended oral anticoagulation, analysis revealed that among factor V carriers the number of major haemorrhages induced by oral anticoagulants would exceed that of clinical pulmonary emboli prevented over the entire range of duration of anticoagulation (1 to 5 years). On the other hand, the number of recurrent deep vein thrombi prevented would exceed that of iatrogenic major bleedings. CONCLUSION: The lack of evidence of a net clinical benefit of prolonged oral anticoagulation, at least beyond 1 year, among patients recovering from acute deep vein thrombosis does not support the decision to promote widespread genetic screening programmes to detect the factor V mutation.