Are factor V Leiden carriers who use oral contraceptives at extreme risk for venous thromboembolism?
BACKGROUND
Major concern was raised by an earlier study regarding oral contraceptive use in women with the factor V Leiden mutation. A more than 30-fold increase in relative risk for venous thromboembolism was reported; for homozygotes, the relative risk was as much as 100-fold or more.


OBJECTIVE
To replicate the reported risk estimates with a new population-based case-control study.


METHODS
Eighty women with a diagnosis of venous thromboembolism were consecutively identified and compared with population-based controls (n = 406). Factor V Leiden mutation was identified by genotype analysis. The evaluation was performed with conditional logistic regression (matched for 5-year age group).


RESULTS
Matched, adjusted odds ratios (OR) for idiopathic venous thromboembolism in women without and with the factor V Leiden mutation who used oral contraceptives were 4.1 (95% confidence interval (CI) 2.1-7.8) and 10.2 (95% CI 1.2-88.4), respectively. The adjusted OR for factor V Leiden carriers was 2.0 (95% CI 1.0-4.4). The OR for women with the factor V Leiden mutation and oral contraceptive use versus no factor V Leiden mutation and no oral contraceptive use was 10.2 (95% CI 3.8-27.6).


CONCLUSIONS
The results confirm the increased relative risk of idiopathic venous thromboembolism for users of oral contraceptives and factor V Leiden carriers. However, we suspect that the true risk for women who are factor V Leiden carriers may be increased two- to four-fold rather than seven-fold or more, and that the risk for the combination of factor V Leiden and oral contraceptive use may be increased in the order often- to 15-fold rather than over 30-fold.
Spannagl
M
M
Ludwig-Maximilian University, Department of Hemostasiology, City Center Clinic, Medical Hospital, Munich, Germany.
Heinemann
L A
LA
Schramm
W
W
D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D015331:Cohort Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D000075202:Contraindications; D005165:Factor V / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease; D005858:Germany / Q000453:epidemiology; D006579:Heterozygote; D006801:Humans; D008875:Middle Aged; D016017:Odds Ratio; D012306:Risk; D013923:Thromboembolism / Q000139:chemically induced* / Q000453:epidemiology / Q000235:genetics; D020246:Venous Thrombosis / Q000139:chemically induced* / Q000453:epidemiology / Q000235:genetics
D003276:Contraceptives, Oral; D005165:Factor V