Increased titer of anti-beta2-glycoprotein I IgG antibody among factor V Leiden carriers during oral contraceptive use.

The risk of thromboembolism during oral contraceptive (OC) use is increased among factor V Leiden (FVL) carriers compared to women with wild-type genotype of the gene for coagulation factor V (FV). The carrier frequency in the general population is too high for FVL alone to be responsible for the reported association. Additional risk factors may be required to explain the increased risk of thromboembolism of carriers during OC use. We conducted a case-control study to compare the titer of anti-beta2-glycoprotein I immunoglobulin G (IgG) and the frequency of elevated titer of IgG type anti-beta2-glycoprotein I antibody between FVL carriers and individuals with FV wild-type genotype with and without pill use. An asymptomatic population of 313 unrelated nonpregnant women were screened for FVL and for the presence of anti-beta2-glycoprotein I IgG antibody. Sixty-six women were FVL carriers and 247 had normal genotype. One-hundred and thirty-five women used OC at the time of screening and 178 did not. Among FVL carriers, OC pill users had a higher mean anti-beta2-glycoprotein I IgG titer than nonusers (9.2 SGU/mL vs. 4.7 SGU/mL, p = 0.0485). Among women with FV wild-type genotype, there was no significant difference in anti-beta2-glycoprotein I IgG titers between users and nonusers of OCs (6.4 SGU/mL and 6.0 SGU/mL, respectively; p = 0.7010). The odds of an elevated anti-beta2-glycoprotein I IgG titer during OC use in FVL heterozygous women was 2.41 (95% confidence interval: 0.79-7.39) relative to users with-type genotype. FVL may contribute to the development of elevated titer of IgG type anti-beta2-glycoprotein I antibody during OC use. The elevated titer of IgG type anti-beta2-glycoprotein I antibody may select women among FVL carriers during OC use with an increased risk of thromboembolism.