Length of exposure to antiphospholipid antibodies, rather than age, is a risk factor for thrombosis: a retrospective single-centre observational study

To investigate the association of age and other factors with thrombosis risk in antiphospholipid antibody (aPL) carriers, a retrospective observational study was conducted in a cohort of patients with medium-high aPL titres recruited in a tertiary care hospital. Assuming an age difference of 9.8 years between patients with and without thrombosis, we estimated that a sample size of 70 participants was required. Several variables besides age including gender, vascular risk factors, inherited thrombophilias, non-thrombotic clinical manifestations, laboratory parameters, aPL profile, length of aPL exposure, antithrombotic drugs and partial aPL score were assessed by univariate analysis followed by multivariate logistic regression. Outcomes were analysed by whether thromboses occurred before (model 1) or after (model 2) aPL detection. Seventy patients [50 females; median (interquartile range) baseline age: 46.99 (39.39-66.20) years] were followed for 2.59 (0.67-5.86) years. Overall, 18 and 5 thromboses were diagnosed applying models 1 and 2, respectively. Time to thrombosis after aPL detection was 2.10 (1.03-8.24) years. Age did not differ between patients with and without thrombosis using models 1 (p = 0.92) or 2 (p = 0.67). Instead, we identified other predictors of thrombosis, namely, lack of thromboprophylaxis [odds ratio (OR) 13.50, 95% confidence interval (95% CI) 1.02-178.05, p = 0.048] and length of aPL exposure (OR 1.41, 95% CI 1.04-1.92, p = 0.026) in model 2, while lupus anticoagulant showed a tendency to increase the risk (OR 7.10, 95% CI 0.86-58.78, p = 0.069) in model 1. Unlike age, lack of thromboprophylaxis, prolonged aPL exposure and lupus anticoagulant may increase the risk of thrombosis in aPL carriers.