Hyperhomocysteinaemia and the risk of recurrent venous thrombosis: results from the MEGA follow-up study.

The measurement of homocysteine is still part of routine thrombosis or thrombophilia work-up in many thrombosis centres in the world. Previous observational studies have shown that hyperhomocysteinaemia is associated with an increased risk of first and recurrent venous thrombosis (VT). Randomised trials, however, showed no benefit of homocysteine-lowering therapy on the risk of first or recurrent VT. This discrepancy could be explained by incomplete adjustment for confounders in the observational studies. We investigated in a large population-based follow-up study whether if the levels of homocysteine and its metabolites, methionine and cysteine, were associated with recurrent VT. Approximately three months after discontinuation of anticoagulant treatment, homocysteine, methionine and cysteine concentrations were measured in 2210 patients with VT. During a median follow-up of 6·9 years, 340 patients developed a recurrence (incidence rate, 2·8/100 patient-years). We found that elevated homocysteine concentrations were not associated with an increased risk of recurrent VT, neither as a continuous variable per 5 μmol/l increase (hazard ratio [HR] 0·98 (95% confidence interval [CI], 0·90-1·04)) nor when levels were >95th (>23·0 μmol/l) percentile (HR 1·03 (95% CI, 0·65-1·64)). Similar results were obtained for cysteine and methionine values. We conclude that hyperhomocysteinaemia is not associated with an increased risk of recurrent VT.