Test–retest reliability, validation, and “minimal detectable change” scores for frequently reported tests of objective physical function in patients with non-dialysis chronic kidney disease

ABSTRACT

Physical function is an important outcome in chronic kidney disease (CKD). We aimed to establish the reliability, validity, and the “minimal detectable change” (MDC) of several common tests used in renal rehabilitation and research. In a repeated measures design, 41 patients with CKD not requiring dialysis (stage 3b to 5) were assessed at an interval of 6 weeks. The tests were the incremental shuttle walk test (ISWT), “sit-to-stand” (STS) test, estimated 1 repetition maximum for quadriceps strength (e1RM), and VO_2peak by cardiopulmonary exercise testing (CPET). Reliability was assessed using intraclass correlation coefficient and Bland–Altman analysis, and absolute reliability by standard error of measurement and MDC. The ISWT, STS-60, e1RM, and CPET had “good” to “excellent” reliability (0.973, 0.927, 0.927, and 0.866), respectively. STS-5 reliability was poor (0.676). The MDC is ISWT, 20 m; STS-5, 7.5 s; STS-60, 4 reps; e1RM, 6.4 kg; VO_2peak, 2.8 ml/kg/min. There was strong correlation between the ISWT and VO_2peak (r = 0.73 and 0.74). While there was poor correlation between the STS-5 and e1RM (r = 0.14 and 0.47), better correlation was seen between STS-5 and ISWT (r = 0.55 and 0.74). In conclusion, the ISWT, STS-60, e1RM, and CPET are reliable tests of function in CKD. The ISWT is a valid means of exercise capacity. The MDC can help researchers and rehabilitation professionals interpret changes following an intervention.

KEYWORDS:

• Chronic kidney diseases
• muscle strength
• outcome assessment
• rehabilitation
• renal insufficiency
• walking

Acknowledgments

The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the National Institute for Health Research Leicester BRC or the Department of Health. We would like to thank Ms. Amy Clarke, Mr. Darren Churchward, Mr. Patrick Highton, and Ms. Charlotte Grantham, researchers at the Leicester Kidney Exercise Team, for collection of some assessment outcome data. At the time of writing this manuscript, Dr. Emma Watson was supported by a Kidney Research UK Post-Doctoral Fellowship. Dr. Barbara Vogt was sponsored by the CAPES Foundation within the Ministry of Education, Brazil. This analysis forms part of a larger body of work being completed by our group (Watson et al., 2018; ISRCTN registration number: 36489137).

Declaration of Interest

The authors report no conflicts of interest.

Additional information

Funding

We are grateful to the Stoneygate Trust for part-funding of this work. The research was supported by the National Institute for Health Research (NIHR), Leicester Biomedical Research Centre (BRC).