Assessment of physical activity in chronic kidney disease.
BACKGROUND
Physical inactivity plays an important role in the development of kidney disease and its complications; however, the validity of standard tools for measuring physical activity (PA) is not well understood.


STUDY DESIGN
We investigated the performance of several readily available and widely used PA and physical function questionnaires, individually and in combination, against accelerometry among a cohort of chronic kidney disease (CKD) participants.


SETTING AND PARTICIPANTS
Forty-six participants from the Seattle Kidney Study, an observational cohort study of persons with CKD, completed the Physical Activity Scale for the Elderly, Human Activity Profile (HAP), Medical Outcomes Study SF-36 questionnaire, and the Four-week Physical Activity History questionnaires. We simultaneously measured PA using an Actigraph GT3X accelerometer during a 14-day period. We estimated the validity of each instrument by testing its associations with log-transformed accelerometry counts. We used the Akaike information criterion to investigate the performance of combinations of questionnaires.


RESULTS
All questionnaire scores were significantly associated with log-transformed accelerometry counts. The HAP correlated best with accelerometry counts (r(2) = 0.32) followed by SF-36 (r(2) = 0.23). Forty-three percent of the variability in accelerometry counts data was explained by a model that combined the HAP, SF-36, and Four-week Physical Activity History questionnaires.


CONCLUSION
A combination of measurement tools can account for a modest component of PA in patients with CKD; however, a substantial proportion of PA is not captured by standard assessments.