Abstract
BACKGROUND AND OBJECTIVES: Muscle wasting is common among patients with ESRD, but little is known about differences in muscle mass in persons with CKD before the initiation of dialysis. If sarcopenia was common, it might affect the use of body mass index for diagnosing obesity in people with CKD. Because obesity may be protective in patients with CKD and ESRD, an accurate understanding of how sarcopenia affects its measurement is crucial. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Differences in body composition across eGFR categories in adult participants of the National Health and Nutrition Examination Survey 1999-2004 who underwent dual-energy x-ray absorptiometry were examined. Obesity defined by dual-energy x-ray absorptiometry versus body mass index and sarcopenia as a contributor to misclassification by body mass index were examined. RESULTS: Sarcopenia and sarcopenic obesity were more prevalent among persons with lower eGFR (P trend <0.01 and P trend <0.001, respectively). After multivariable adjustment, the association of sarcopenia with eGFR was U-shaped. Stage 4 CKD was independently associated with sarcopenia among participants ≥60 years old (adjusted odds ratio, 2.58; 95% confidence interval, 1.02 to 6.51 for eGFR=15-29 compared with 60-89 ml/min per 1.73 m(2); P for interaction by age=0.02). Underestimation of obesity by body mass index compared with dual-energy x-ray absorptiometry increased with lower eGFR (P trend <0.001), was greatest among participants with eGFR=15-29 ml/min per 1.73 m(2) (71% obese by dual-energy x-ray absorptiometry versus 41% obese by body mass index), and was highly likely among obese participants with sarcopenia (97.7% misclassified as not obese by body mass index). CONCLUSIONS: Sarcopenia and sarcopenic obesity are highly prevalent among persons with CKD and contribute to poor classification of obesity by body mass index. Measurements of body composition beyond body mass index should be used whenever possible in the CKD population given this clear limitation.