Background: Most techniques for measuring body composition are based on 2-component models (2-CMs) and depend on assumptions relating to the constancy of the density (D(FFM)) and hydration fraction (HF(FFM)) of fat-free mass (FFM).
Objectives: The objectives were to determine whether these assumptions are systematically violated in patients with cirrhosis and to assess the validity of the estimates of body composition obtained in these patients by using 2-CM techniques.
Design: Body composition was assessed by using a 4-component model (4-CM), which was based on data obtained from densitometry, deuterium dilution, and dual-energy X-ray absorptiometry, in 20 patients with cirrhosis who had no evidence of fluid retention and in 20 pair-matched healthy control subjects. The results were compared with those obtained by using "reference" and "bedside" 2-CM techniques.
Results: The mean (+/-SD) D(FFM) was significantly lower in the patients with cirrhosis (1.091 +/- 0.008 compared with 1.100 +/- 0.006 kg/L; P < 0.001); no significant difference in HF(FFM) was observed between the patients and control subjects (74.5 +/- 2.6 compared with 73.5 +/- 2.1), although there was greater variability in the patients. Significant differences were observed in the body-composition variables obtained by using the "reference" 2-CM techniques compared with the 4-CM-the 95% limits of agreement in the patients with cirrhosis exceeded 5% body fat and 3 kg FFM; the corresponding values for the "bedside" 2-CM techniques were 11% body fat and 7.5 kg FFM.
Conclusions: Assumptions relating to the constancy of the D(FFM) and HF(FFM) are violated in patients with cirrhosis. Thus, standard 2-CM techniques provide inaccurate body composition estimates in this patient population.