Sources of Variation in Estimates of Lean Body Mass by Creatinine Kinetics and by Methods Based on Body Water or Body Mass Index in Patients on Continuous Peritoneal Dialysis
published online 23 October 2009.
Objective
We identified factors that account for differences between lean body mass computed from creatinine kinetics (LBMcr) and from either body water (LBMV) or body mass index (LBMBMI) in patients on continuous peritoneal dialysis (CPD).
Design
We compared the LBMcr and LBMV or LBMBMI in hypothetical subjects and actual CPD patients.
Patients
We studied 439 CPD patients in Albuquerque, Pittsburgh, and Toronto, with 925 clearance studies.
Intervention
Creatinine production was estimated using formulas derived in CPD patients. Body water (V) was estimated from anthropometric formulas. We calculated LBMBMI from a formula that estimates body composition based on body mass index. In hypothetical subjects, LBM values were calculated by varying the determinants of body composition (gender, diabetic status, age, weight, and height) one at a time, while the other determinants were kept constant. In actual CPD patients, multiple linear regression and logistic regression were used to identify factors associated with differences in the estimates of LBM (LBMcr<LBMV, or LBMcr<LBMBMI).
Main Outcome Measure
We sought predictors of the differences LBMV – LBMcr and LBMBMI – LBMcr.
Results
Both LBMV (regardless of formula used to estimate V) and LBMBMI exceeded LBMcr in hypothetical subjects with average body compositions. The sources of differences between LBM estimates in this group involved differences in the coefficients assigned to gender, age, height, weight, presence or absence of diabetes, and serum creatinine concentration. In CPD patients, mean LBMV or LBMBMI exceeded mean LBMcr by 6.2 to 6.9 kg. For example, the LBMV obtained from one anthropometric formula was 50.4±10.4 kg and the LBMcr was 44.1±13.6 kg (P < .001), whereas among the 925 clearance studies, only 216 (23.3%) had LBMcr>LBMV. The differences in determinants of body composition between groups with high versus low LBMcr were similar in hypothetical and actual CPD patients. Multivariate analysis in actual CPD patients identified serum creatinine, height, age, gender, weight, and body mass index as predictors of the differences LBMV−LBMcr and LBMBMI−LBMcr.
Conclusions
Overhydration is not the sole factor accounting for the differences between LBMcr and either LBMV or LBMBMI in CPD patients. These differences also stem from the coefficients assigned to major determinants of body composition by the formulas estimating LBM.
∗Nephrology Section, Raymond G. Murphy Veterans Administration Medical Center and University of New Mexico, Albuquerque, New Mexico
†Epidemiology Section, Raymond G. Murphy Veterans Administration Medical Center and University of New Mexico, Albuquerque, New Mexico
‡Nephrology Division, University of Pittsburgh, Pittsburgh, Pennsylvania
§Nephrology Division, George Washington University, Washington, D.C
¶Department of Biochemistry and Molecular Biology, University of New Mexico, Albuquerque, New Mexico
#Nephrology Division, University of Pittsburgh, Pittsburgh, Pennsylvania
∫Nephrology Section, Raymond G. Murphy Veterans Administration Medical Center, and University of New Mexico, Albuquerque, New Mexico
∥Nephrology Section, Raymond G. Murphy Veterans Administration Medical Center, and University of New Mexico, Albuquerque, New Mexico
∼Department of Medicine, University of Toronto, Toronto, Ontario, Canada
Address reprint requests to Antonios H. Tzamaloukas, Renal Section (111C), Raymond G. Murphy Veterans Administration Medical Center, 1501 San Pedro SE, Albuquerque, NM 87108.
This work was performed at the Service of Medicine, Raymond G. Murphy Veterans Administration Medical Center, and Department of Medicine, School of Medicine, University of New Mexico, Albuquerque, New Mexico; the Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania; and the Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
ABSTRACT