Disease activity, quality of life and indirect costs of reduced productivity at work, generated by Polish patients with ankylosing spondylitis

OBJECTIVES The aim of the study was to investigate the association between activity of ankylosing spondylitis (AS) and decrease in quality of life as well as productivity loss of affected patients in a specified group of patients in the Polish setting. MATERIAL AND METHODS An questionnaire survey was conducted using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) to assess disease activity, as well as the Work Productivity and Activity Impairment Questionnaires to assess productivity loss; quality of life was presented as utility calculated using the EuroQol 5 questionnaire and also measured on a visual analogue scale (VAS). Indirect costs were assessed with the human capital approach implying gross domestic product per capita or gross value added per worker in Poland in 2014 and were expressed in Polish zlotys (PLN) as well as in euros. Correlation was presented using Spearman's rank correlation coefficient. RESULTS We performed our analysis based on 78 full questionnaires collected. A mean BASDAI score of 5.91 in the analysed group of patients was detected and mean utility of 0.5135 was observed. Average quality of life measured on the visual analogue scale was 46.55. Mean number of days off work was 45.26 days per year and mean on-the-job productivity loss was 49.29%. Average annual indirect costs per patient were €4241 (17 686 PLN) calculated using gross domestic product and €10 172 (42 417 PLN) estimated using gross value added. Total productivity loss was significantly correlated with disease activity (strong correlation of 0.6005) and utility (moderate correlation of -0.3698). CONCLUSIONS Ankylosing spondylitis causes a great decrease in quality of life as well as patients' productivity loss associated with both absenteeism and presenteeism. The greater the disease activity is, the lower is the utility, the lower is the quality of life measured on the VAS, and the greater are the total annual indirect costs. Total indirect costs were negatively correlated with utility; although the association was moderate, it was significant.