Test–Retest Reliability of a Performance-Based Test Battery in Patients with Fibromyalgia According to Socio-Occupational Status

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.