Test–Retest reliability of a performance-based test battery in patients with fibromyalgia according to socio-occupational status

Abstract

Background: Performance-based tests (PBTs) objectively assess functional capacity and are increasingly applied in fibromyalgia (FM) to complement patient-reported outcomes (PROMs). However, evidence regarding their reliability, especially considering patients’ socio-occupational status, is limited. This study aimed to determine test–retest reliability of a standardized PBT battery in women with FM and to examine the influence of employment status on measurement stability. Methods: A total of 119 women were assessed (89 with FM). The battery included the 6 min walk test (6MWT), handgrip strength test (HST), and 8 feet up and go test (8FUGT). Test–retest reliability was examined using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and smallest real difference (SRD). Analyses were conducted for the total FM group and socio-occupational subgroups (actively working, claiming disability, and permanent disability). Results: All PBTs demonstrated excellent test–retest reliability. Measurement stability was consistently higher in controls. Absolute reliability indices confirmed acceptable measurement stability. However, the claiming disability group showed markedly higher SEM% and SRD% for HST, suggesting reduced reproducibility. The 6MWT and 8FUGT maintained excellent reliability and stability across all groups. PROMs showed good-to-excellent reliability. Conclusions: PBTs showed excellent reliability in women with FM. However, reliability varied across socio-occupational groups, particularly for HST in patients claiming disability. PROMSs showed lower reliability than PBTs.