Association of Body Composition with Survival Among Patients on Hemodialysis

Several years ago, an “obesity paradox” was reported among several different cohorts of patients who were on dialysis (1–4). It soon became apparent that patients with high body mass index (BMI), even at levels considered obese and morbidly obese, had better survival than patients whose BMI was in the normal range (5). Although BMI is strongly correlated with percentage of body fat, including among patients who are on dialysis, it does not allow for the separation of fat and lean in an individual because it is calculated only from height and weight. Nevertheless, the improved survival among even those with extremely high BMI suggested that being fatter was truly advantageous. Individuals with higher BMI and higher body fat usually also have higher lean body mass than those with low BMI, so the question of which component of body composition—fat or lean—is associated (or is more associated) with the observed obesity paradox became a point of debate, contention, and, of course, further research. Initial attempts to use creatinine generation, calculated from 24-hour creatinine data reported on the Centers for Medicare and Medicaid Medical Evidence Form 2728, yielded contradictory results (5,6). One analysis showed that adjustment for creatinine generation did not mitigate the high BMI survival advantage (5), but another showed that patients with high BMI but creatinine generation (as a proxy for muscle mass) in the lowest quartile did not have a survival advantage and argued that the survival advantage of high BMI was limited to patients with normal or high muscle mass (6). Still other investigators called into question the use of these data on the basis that the quality may be low, with some providers reporting a creatinine-based estimated GFR rather than a measured creatinine clearance (7). Furthermore, even with reporting of true creatinine clearance, incomplete urine collections could lead to underestimation of creatinine generation and, thus, underestimation of muscle mass. More sophisticated measures of body composition or parameters that can be used to estimate body composition are needed to address whether higher muscle mass, body fat, or both are associated with longer survival among patients who are on dialysis. However, direct measurement of body composition is