Outcomes of genetic testing in adults with a history of venous thromboembolism.

OBJECTIVE: To address whether Factor V Leiden (FVL) testing alone, or in combination with prothrombin G20210A testing, leads to improved clinical outcomes in adults with a personal history of venous thromboembolism (VTE) or to improved clinical outcomes in adult family members of mutation-positive individuals. DATA SOURCES: Searches of MEDLINE, EMBASE, The Cochrane Library, the Cumulative Index to Nursing and Allied Health Literature, and PsycInfo through December 2008. REVIEW METHODS: We focused on the analytic validity, clinical validity, and clinical utility of these tests. Each included article underwent double review for data abstraction and assessment of study quality. We pooled the results of studies addressing the clinical validity of these tests when there were sufficient data. Other evidence was summarized in evidence tables. We graded the evidence by adapting a scheme recommended by the Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group by assessing the limitations affecting individual study quality, the certainty regarding the directness of the observed effects in the studies, the precision and strength of the findings, and the availability (or lack) of data to answer the relevant key question. Evidence for each sub-question was graded as high, moderate, or low. RESULTS: We reviewed 7,777 titles and included 124 articles. No direct evidence addressed the primary objective. However, high-grade evidence supported the conclusion that tests for the detection of FVL and prothrombin G20210A have excellent analytic validity. Most clinical laboratories test for these mutations accurately. Heterozygosity [odds ratio (OR) =1.56 (95 percent confidence interval (CI) 1.14 to 2.12)] and homozygosity [OR=2.65 (95 percent C.I. 1.2 to 6.0)] for FVL in probands are predictive of recurrent VTE. Heterozygosity for FVL predicts VTE in family members [OR=3.5 (95 percent C.I. 2.5 to 5.0)] as does homozygosity for FVL [OR=18 (95 percent C.I. 7.8 to 40)]. Heterozygosity for prothrombin G20210A is not predictive of recurrence in probands [OR=1.45 (95 percent C.I. 0.96-2.2)]. Evidence is insufficient about heterozygosity for prothrombin G20210A in family members and insufficient about homozygosity for prothrombin G20210A. A single study supported the hypothesis that clinicians might change management based on test results. There was high-grade evidence that anticoagulation reduces recurrent events in probands with FVL or prothrombin G20210A, however, there was low-grade evidence that the relative reduction with treatment is comparable to that seen in individuals without mutations. There was moderate evidence to support the conclusion that neither harms nor benefits of testing have been demonstrated conclusively. Decision-analysis models suggest that testing may be cost-effective in select individuals. CONCLUSIONS: There is no direct evidence that testing for these mutations leads to improved clinical outcomes in adults with a history of VTE or their adult family members. The literature supports the conclusion that while these assays have high analytic validity, the test results have variable clinical validity for predicting VTE in these populations and have only weak clinical utility.