Metabolic index in peritoneal dialysis

To define protein anabolism or catabolism in our patients we retrospectively studied the 24-hour balances (B24 h), dietary protein intake (DPI), anthropometric parameters [body mass index (BMI), tricipital skin fold thickness (TF), and muscular arm circumference (MAC), using the rating scheme: undernourished (U): percentile (pc) < 15; normal (N): pc > 15 to pc < 85; obese (O): pc > 85], and urea kinetics (protein equivalent of nitrogen appearance) [PNA = PCR according to the Gotch-Borah (G), Blumenkrantz (B), and Randerson (R) formulas]. Nitrogen-balance [N-B = DPI(N)-PNA(N)], metabolic ratio (MR = DPI/PNA), and metabolic index (MI = IDPI/nPNA) were calculated as metabolic indicators. There were 215 evaluations (B24 h) in 44 patients, of whom 29 were male and 15 female, 35 on continuous ambulatory peritoneal dialysis (PD), 9 on automated PD, age 58.2 +/- 15.6 years, followed-up for 15.3 +/- 10.2 months. Undernourished patients (BMI) showed higher N-B, MR, and MI irrespective of the formula used, but MR was only significant using the Blumenkrantz formula. For N-balance and metabolic index, analysis of variance (ANOVA) was significant with all formulas. The mean metabolic index (Randerson) in subgroups was: U: 1.09 +/- 0.27, n = 54; N: 0.90 +/- 0.25, n = 135; O: 0.87 +/- 0.27, n = 26 (ANOVA: P < 0.0001). The U-N and U-O subgroup comparison was significant (Newman-Keuls P < 0.01). We concluded that: (1) The metabolic index is more discriminating for protein metabolism than N-balance or metabolic ratio. (2) Most of the undernourished patients (BMI) are anabolic according to metabolic index and N-balance, and this indicates recovery. (3) Undernourished (low BMI) patients with metabolic index < 1 deserve special attention due to the risk of remaining malnourished.