Authors' objectives:

Factor V Leiden is the most common hereditary blood coagulation disorder. It is present in 3-8% of a healthy white population and it is associated with venous thrombosis especially in oral contraceptive users. The author evaluates a proposal to introduce screening for Factor V Leiden mutation in oral contraceptive users who have a first degree relative who has suffered venous thrombosis, and deter test positives from oral contraception, in comparison with standard practice of deterring on the basis of family history only.

Authors' results and conclusions: One study found that the combination of the use of oral contraceptives and carriage of the Factor V Leiden mutation strongly increases the risk of thrombosis. A group of 155 pre-menopausal women with thrombosis were compared with 169 controls. There was a four-fold increase in relative risk of thrombosis in oral contraceptive users. Carriers of Factor V Leiden mutation had an eight-fold increased risk of thrombosis. The other study was more ambiguous: the authors found that new low-dose oral contraceptives have a higher associated risk of thrombosis than previous oral contraceptives. This effect is enhanced by Factor V Leiden mutation, with risk increased almost 50-fold compared to non-carrier non-users, and by a family history of thrombosis. However, neither explains all the excess risk of a third-generation pill, and there are other moderate to strong independent risk factors.

Authors' recommendations: The author concludes that there is no direct evidence to support the introduction of screening high risk users of oral contraceptives for Factor V Leiden. Potential benefits include reduced risk of thrombosis and more reliable contraception, but disbenefits include increased risk of thrombosis and reduced choice of contraception, in different groups of women. The caveat is added that this is a fast-developing technology and its use may become more desirable as its accuracy improves.

Authors' methods: Review

Project Status: Completed

URL for project: http://www.wihrd.soton.ac.uk

Year Published: 1996

English language abstract: An English language summary is available

Publication Type: Not Assigned

Country: England

Organisation Name: Wessex Institute for Health Research and Development

Contact Address: Pauline King. Wessex Institute for Health Research and Development, Boldrewood Medical School, Bassett Crescent East, Highfield, Southampton. SO16 7PX Tel. +44 1703 595661 Fax +44 1703 595662

Copyright: Wessex Institute for Health Research and Development (WIHRD)