Risk prediction of recurrent venous thrombosis; where are we now and what can we add?

Background Several models are available to predict recurrent venous thrombosis (VT) in patients with unprovoked first events. Objectives To validate these prediction models externally. Methods Within the MEGA follow‐up study (n = 3750), we externally validated the Vienna and DASH score. These models were validated (a) by using the original study's criteria for patients with unprovoked VT and (b) by using our own criteria for unprovoked VT. In addition, absolute recurrence risks based on individual VT risk factors were calculated. Results The recurrence rate was 5.2 (95% CI, 4.6‐5.9) per 100 patient‐years in those who had a first unprovoked VT according to our definition. For the Vienna model it was 3.4 per 100 patient‐years and for DASH 3.8 per 100 patient‐years. The C‐statistic was 0.62 for Vienna and 0.65 for DASH. The C‐statistic declined to 0.58 for both Vienna and DASH when we used our own definition of “unprovoked VT.” Within the provoked group a strong gradient in risk was found dependent on the presence of traditional risk factors or biomarkers in a patient. Conclusions The ability to distinguish patients’ recurrence risks is lower than proposed in the original prediction model studies and dependent on the definition that is used for an unprovoked first event. Furthermore, our results suggest that a more‐refined risk estimation is possible, also in patients with a provoked first event, who are currently all classified as low risk.