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

Abstract

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.

Keywords: absenteeism; ankylosing spondylitis; longitudinal; sick leave.

Figure 1

Distribution of first and recurrent sick leave episodes over time in the study population at risk. No SL yet=those who are at risk for sick leave, but have not incurred any sick leave (yet). First SL=those who reported SL for the first time during follow-up, in the previous interval or before. Recurrent SL=those who reported SL for the second time during follow-up, in the previous interval or before. Censored=censored from analyses due to reasons of job loss, unemployment, work disability, retirement. Lost to follow-up=patients that were lost to follow-up. *Due to the design of OASIS (annual assessments until month 72, thereafter every 2 years), annual assessments were not always available for those who became at risk for SL during follow-up. AS, ankylosing spondylitis; LTFU, lost to follow-up; OASIS, Outcome in Ankylosing Spondylitis International Study; SL, ankylosing spondylitis-related sick leave.