Unprovoked recurrent venous thrombosis: prediction by D-dimer and clinical risk factors.

Summary. Background: The aim of the study was to determine the predictive value of D-dimer measurement for unprovoked recurrent venous thrombosis and the influence of sex, age and type of first event (unprovoked or provoked). Methods: Prospective cohort study of 272 patients with a first episode of venous thrombosis that was unprovoked or provoked by a non-surgical trigger. Findings: The cumulative rate of unprovoked recurrence in patients with a positive D-dimer was 20% at 5 years [5.5/100 patient-years, 95% confidence interval (CI) 3.7–7.8] and in patients with a negative D-dimer 17% (4.1/100 patient-years, 95% CI 2.3–6.9). The rates are not different (hazard ratio 1.3, 95% CI 0.7–2.5). After adjustment for clinical risk factors a positive D-dimer result was significantly associated with an increased risk of unprovoked recurrent thrombosis (hazard ratio 2.0, 95% CI 1.01–3.9). The strongest indicator of risk of recurrence was male sex (hazard ratio 3.3 unadjusted and 2.9 after adjustment). The only determinant of D-dimer in a linear regression model was age (P < 0.001). Conclusions: The analysis indicates that clinical risk factors confound the association between D-dimer and risk of recurrence and when adjusted for these confounders a positive D-dimer result is significantly associated with unprovoked recurrence. The clinical utility of D-dimer measurement in individual patients should be interpreted in conjunction with clinical risk factors.