Prevalence of confirmed antiphospholipid syndrome in 18-50 years unselected patients with first unprovoked venous thromboembolism.

A total of 524 incident patients aged 18 to 50 years were included in the anticoagulation clinic during the study period. Of them, 491 were tested for APS and 44 (9.0%; 95% confidence interval [CI]: 6.7-11.8) fulfilled APS criteria. Of 26 APS women, 8 (30.8%) were on combined oral contraceptive pill at the time of VTE, versus 108 (55.1%) in non-APS women (P = .02). No difference was observed between APS and non-APS patients in terms of gender or type of VTE. The prevalence of APS is high in young patients with a first unprovoked VTE. In the direct oral anticoagulant era, when and how to test for APS is challenging and deserves further investigation.