RESUMO
BACKGROUND: We aimed to validate and to refine current recurrent venous thromboembolism (VTE) risk classification. METHODS: We performed a post hoc analysis of a multicentre cohort including 1881 patients with a first symptomatic VTE prospectively followed after anticoagulation discontinuation. The primary objective was to validate the International Society of Thrombosis and Haemostasis (ISTH) risk classification in predicting recurrence risk. The secondary objective was to evaluate a refined ISTH classification based on the recurrence risk estimate for each individual risk factor. RESULTS: During a 4.8-year median follow-up after anticoagulation discontinuation, symptomatic recurrent VTE occurred in 230 patients (12.2%). Based on the ISTH classification, patients with unprovoked VTE or VTE with minor or major persistent risk factors had a 2-fold increased recurrence risk compared with those with VTE and major transient risk factors. Recurrence risk was not increased in patients with minor transient factors (hazard ratio (HR) 1.31, 95% CI 0.84-2.06). Individual risk factors analysis identified hormone-related VTE (pregnancy: HR 0.26, 95% CI 0.08-0.82; oestrogens: HR 0.25, 95% CI 0.14-0.47) and amyotrophic lateral sclerosis (HR 5.84, 95% CI 1.82-18.70). After reclassification of these factors as major transient for the former and major persistent for the latter, the modified ISTH classification allowed us to accurately discriminate between patients at low risk of recurrence (i.e. with major transient risk factors) and those at high risk of recurrence (i.e. without major transient risk factors). CONCLUSIONS: Among patients who stopped anticoagulation after a first VTE, a refined ISTH classification based on recurrence risk intensity of individual factors allowed discrimination between patients at low recurrence risk, including hormonal exposure in women, and patients at high recurrence risk.