Test-retest repeatability for Fatigue Assessment Scale, Short-Form 6-Dimension and King’s Sarcoidosis Questionnaire in people with sarcoidosis associated fatigue

Background and aim: Patient related outcomes are important in sarcoidosis, but the medium-term repeatability of the key patient reported outcome measure is not known. We aimed to test the repeatability of the Fatigue Assessment Scale (FAS), Short Form 6-Dimension (SF-6D), and King’s Sarcoidosis Questionnaire (KSQ) in free living people with sarcoidosis associated fatigue. Methods: Twelve people with sarcoidosis associated fatigue completed the FAS, short form 36 questionnaire (SF-36) and the KSQ at baseline and 12 weeks. The SF-6D utility was calculated from the SF-36. The difference between baseline and 12 week assessments was measured. Results: The interclass correlation (95% confidence interval) showed good agreement between the baseline and 3 months measurements: FAS 0.91 (0.74, 0.71), SF-36 0.98 (0.94, 1), KSQ 0.98 (0.93, 0.99), SF-6D utility 0.98 (0.93, 0.99). The baseline (standard deviation) FAS was 27.83 (5.86) and at 12 weeks was 27.25 (7.55) representing a 0.58 difference (95% CI for difference (-1.89, 3.06)), SF-6D utility was 0.69 (0.16) at baseline and 0.68 (0.17) after 3 months representing at 0.00 (-0.03, 0.03) difference and corresponding values for KSQ were 59.12 (18.68) and 56.91 (27.26) with a difference of -1.87 (5.49,1.76). Conclusions: There was good repeatability of FAS, SF-36, SF-6D and KSQ in free living people with sarcoidosis associated fatigue. Fatigue, general and disease specific health related quality of life showed no significant change over 12 weeks. Studies identifying changes in these outcomes can confidently report a true change and not measurement error or regression to the mean.