Predictors of the post‐thrombotic syndrome with non‐invasive venous examinations in patients 6 weeks after a first episode of deep vein thrombosis

Summary. Background: Post‐thrombotic syndrome (PTS) is a chronic complication of deep vein thrombosis (DVT) affecting a large number of patients. Because of its potential debilitating effects, identification of patients at high risk for the development of this syndrome is relevant, and only a few predictors are known. Objectives: To assess the incidence and potential predictors of PTS. Methods: We prospectively followed 111 consecutive patients for 2 years after a first episode of objectively documented DVT of the leg. With non‐invasive venous examinations, residual thrombosis, valvular reflux, calf muscle pump function and venous outflow resistance were assessed at 6 weeks, 3 months, 6 months, 1 year, and 2 years. The Clinical, Etiologic, Anatomic, and Pathophysiologi classification was used to record the occurrence and severity of PTS. Regression analysis with area under the receiver operating characteristic (ROC) curve was performed to identify potential predictors. Results: The cumulative incidence of PTS was 46% after 3 months, and the incidence and severity did not increase further. Men appeared to be at increased risk as compared with women (risk ratio [RR] 1.4, 95% confidence interval [CI] 0.9–2.2), as were patients over 50 years as compared with younger patients (RR 1.4%, 95% CI 0.9–2.1). Patients with thrombosis localized in the proximal veins at diagnosis had an increased risk of PTS as compared with patients with distal thrombosis (RR 2.3%, 95% CI 1.0–5.6). PTS developed in 32 of 52 patients (62%) with residual thrombosis in the proximal veins 6 weeks after diagnosis, as compared with 17 of 45 patients (38%) without residual proximal thrombosis, leading to a 1.6‐fold increased risk (95% CI 1.0–2.5). The presence of valvular reflux in the superficial veins was also a predictor at 6 weeks, with a 1.6‐fold increased risk as compared with patients without superficial reflux (95% CI 1.1–2.3). A multivariate analysis of these predictors yielded an area under the ROC curve of 0.72 (95% CI 0.62–0.82). Conclusions: PTS develops in half of all patients within 3 months, with no further increase being seen up to 2 years of follow‐up. Male sex, age over 50 years, proximal localization of the thrombus at entry, residual proximal thrombosis and superficial valvular reflux at 6 weeks seem to be the most important predictors of PTS in patients with a first episode of DVT. Duplex scanning 6 weeks after diagnosis appears to be clinically useful for the identification of patients at risk of PTS.