Relative and absolute reliability of physical function measures in people with end-stage renal disease

End-stage renal disease (ESRD) is a condition affecting multiple physiological systems, leading to a decline in physical function. Effectiveness of therapeutic interventions in people with ESRD has been assessed using various functional and activity outcome measures. The purpose of this study was to determine the relative and absolute reliability of the 6-minute walk test (6MWT), timed sit-to-stand in 30 seconds (TSS30), and maximal and adjusted activity scores (MAS-HAP, AAS-HAP) of the Human Activity Profile (HAP) in people with ESRD.

A convenience sample of 25 participants (67.2±14.2 years) was recruited from an outpatient dialysis unit. Relative reliability was determined using the intraclass correlation coefficient (ICC(2,1)), and absolute test-retest reliability with the standard error of measurement (SEM) and minimal detectable change at the 95% confidence interval (MDC(95)) statistics, respectively. The test-retest interval was 1 week.

Relative reliability (ICC(2,1)) was 0.93 for both the 6MWT and the TSS30, 0.92 for the AAS-HAP, and 0.76 for the MAS-HAP. Absolute reliability (SEM and MDC(95)) values for the 6MWT, AAS-HAP, and TSS30 were 28 m and 77 m, 4.1 and 11.4, and 0.9 and 2.6 repetitions, respectively.

Our results suggest that the 6MWT, TSS30, and AAS-HAP are reliable physical function and activity outcome measures in people with ESRD. However, the magnitude of the absolute reliability statistics suggests significant within-participant variability on repeat testing in this population.