Sick leave and its predictors in ankylosing spondylitis: long-term results from the Outcome in Ankylosing Spondylitis International Study

Objective To investigate the occurrence of ankylosing spondylitis (AS)-related sick leave (SL) over 6 12 years and explore factors predicting first and recurrent SL. Methods Data from employed patients from the Outcome in Ankylosing Spondylitis International Study were used. At each visit, patients indicated the occurrence of SL (yes/no) in the previous inter-assessment period. Cox regressions predicted a first episode of SL. Generalised estimating equations (GEE) explored the association between SL and (time-lagged) predictors. To investigate whether SL predicts new SL, SL in the first year was included as covariate in a separate analysis. Results 139 patients (76% males, mean (SD) age 38.7 (10.0) years) were at risk for SL for an average period of 7.9 years, of whom 88 (63%) reported any SL. In both the Cox baseline predictors model (HR (95% CI)) and the time-varying GEE models (OR (95% CI)), AS Disease Activity Score (1.67, 1.23 to 2.28 (HR); 1.48, 1.07 to 2.03 (OR)); Bath AS Disease Activity Index (1.33, 1.18 to 1.51 (HR); 1.31, 1.15 to 1.49 (OR)), Bath AS Functional Index (1.17, 1.02 to 1.34 (HR); 1.31, 1.16 to 1.47 (OR)) and comorbidity at baseline (GEE only, 1.52, 1.00 to 2.29 (OR)) were associated with SL in separate models, but only in patients with low educational attainment. SL in the first year was an independent predictor of SL over time (OR: 2.62 to 8.37 in different models, all p<0.05). Conclusion Disease activity and physical function predicted first and recurrent SL, but only in patients with low educational attainment. Prior SL results in future SL, and SL should therefore be a signal for support to prevent future adverse work outcome.