Utility of Factor V Leiden testing for idiopathic venous thromboembolism is unclear - Patient-Oriented Evidence that Matters

Journal of Family Practice, July, 2002 by Dale E. Korn, James J. Stevermer

Eckman MH, Singh SK, Erban JK, Kao G. Testing for Factor V Leiden in patients with pulmonary or venous thromboembolism: a cost-effective analysis. Med Decis Making 2002; 22:108-24.

* BACKGROUND Factor V Leiden deficiency is associated with an increased risk of initial venous thromboembolism. The prevalence of Factor V Leiden deficiency varies with ethnicity and age of onset of initial venous thromboembolism. If Factor V Leiden deficiency predicts recurrent venous thromboembolism, putting affected patients on extended anticoagulation therapy may be beneficial. This study evaluated the cost effectiveness of testing patients for Factor V Leiden deficiency after initial venous thromboembolism, taking into account costs and complications associated with recurrent venous thromboembolism, compared with ongoing anticoagulation therapy.

* POPULATION STUDIED This study was a decision analysis that assumed a base case of a 35-year-old woman with initial venous thromboembolism. Subpopulations for sensitivity analyses were based on ethnicity, prevalence of Factor V Leiden deficiency, age at onset, precipitating factors for venous thromboembolism, length of therapeutic intervention, and morbidities attributed to anticoagulation. The risk for recurrent venous thromboembolism in patients homozygous for Factor V Leiden deficiency is high; this study focused on heterozygotes, a population whose recurrence risk is less well defined.

* STUDY DESIGN AND VALIDITY This decision analysis used sound methods and the sensitivity analyses were appropriate. It is unclear whether a systematic literature review was performed. A pivotal factor was the assumption of an increased risk of recurrence in patients with Factor V Leiden deficiency as compared with patients without the deficiency. The authors based this assumption on an 8-year study that showed an increased risk of recurrence of 2.4 (95% confidence interval [CI], 1.3-4.5, n = 41). All of the recurrences were detected in the first 3 years. However, other studies, of somewhat shorter duration, demonstrated risk ratios of 1.1 (95% CI, 0.7-1.6, n = 112) within 4 years (1) and 0.5 (95% CI, 0.1-1.8, n = 37) within 2 years. (2)

* OUTCOMES MEASURED The primary outcomes reported were the risk of recurrence of deep venous thrombosis, morbidity associated with therapeutic intervention, and the cost effectiveness of 3 different treatment strategies.

* RESULTS All Factor V Leiden-deficient patients were assumed to have a 7.4% per-year risk of recurrence. Various models were constructed based on the duration of that increased risk. The base case assumed a 0% recurrent deep venous thrombosis risk after 3 years; the modified-base case strategy assumed that patients returned to the population average of 2.3% per year after 3 years; and the constant rate model assumed a continued 7.4% per-year risk of recurrent deep venous thrombosis. In all models, testing and treating for life was most expensive. The base and modified-base models demonstrated testing and treatment for 3 years were the most cost effective. If a patient population has a risk of major hemorrhage of more than 1.9% per year, a low prevalence of Factor V Leiden deficiency, a clear precipitant for venous thromboembolism, or a recurrence risk for venous thromboembolism from Factor V Leiden deficiency of less than 1.9, then testing is not indicated.

RECOMMENDATIONS FOR CLINICAL PRACTICE

If the assumptions made in this study are true, then patients at low risk for long-term anticoagulation should be tested for Factor V Leiden deficiency, and if positive, treated for 3 years, pending longer-term studies. However, studies have not clearly defined an increased risk for recurrent venous thromboembolism in patients with Factor V Leiden deficiency. Until the true relative risk is ascertained, routine screening of patients with initial idiopathic venous thromboembolism for Factor V Leiden deficiency should not be used to determine length of anticoagulation.

REFERENCES

(1.) De Stefano V, Martinelli I, Mannucci PM, et al. The risk of recurrent deep venous thrombosis among heterozygous carriers of both factor V Leiden and the G20210A prothrombin mutation. N Engl J Med 1999; 341:801-6.

(2.) Kearon C, Gent M. Hirsh J, et al. A comparison of three months of anticoagulation with extended anticoagulation for a first episode of idiopathic venous thromboembolism. N Engl J Med 1999; 340:901-7

Dale E. Korn, MD;
and James J. Stevermer, MD, MSPH
Department of Family and Community Medicine
University of Missouri Hospital and Clinics
Columbia
E-mail: kornd@health.missouri.edu