Measurement of body composition in burned children: is there a gold standard?

Abstract

Background: Maintaining lean body mass (LBM) after a severe burn is an essential goal of modern burn treatment. An accurate determination of LBM is necessary for short- and long-term therapeutic decisions. The aim of this study was to compare 2 measurement methods for body composition, whole-body potassium counting (K count) and dual x-ray absorptiometry (DEXA), in a large prospective clinical trial in severely burned pediatric patients.

Methods: Two-hundred seventy-nine patients admitted with burns covering 40% of total body surface area (TBSA) were enrolled in the study. Patients enrolled were controls or received long-term treatment with recombinant human growth hormone (rhGH). Near-simultaneous measurements of LBM with DEXA and fat-free mass (FFM) with K count were performed at hospital discharge and at 6, 9, 12, 18, and 24 months post injury. Results were correlated using Pearson's regression analysis. Agreement between the 2 methods was analyzed with the Bland-Altman method.

Results: Age, gender distribution, weight, burn size, and admission time from injury were not significantly different between control and treatment groups. rhGH and control patients at all time points postburn showed a good correlation between LBM and FFM measurements (R(2) between 0.9 and 0.95). Bland-Altman revealed that the mean bias and 95% limits of agreement depended only on patient weight and not on treatment or time postburn. The 95% limits ranged from 0.1 +/- 2.9 kg for LBM or FFM in 7- to 18-kg patients to 16.3 +/- 17.8 kg for LBM or FFM in patients >60 kg.

Conclusions: DEXA can provide a sufficiently accurate determination of LBM and changes in body composition, but a correction factor must be included for older children and adolescents with more LBM. DEXA scans are easier, cheaper, and less stressful for the patient, and this method should be used rather than the K count.

Figures

Figure 1

Whole-body K-Counter used in this study at the University of Texas Medical Branch.

Figure 2

DEXA scanner used in this study at Shriners Hospitals for Children.

Figure 3

(A) Correlation of lean-body mass (LBM) with fat-free mass (FFM) for all patients (Control + Growth Hormone) across all time points (n=279). (B) Correlation of lean-body mass (LBM) with fat-free mass (FFM) for control patients across all time points. (C) Correlation of lean-body mass (LBM) with fat-free mass (FFM) for growth hormone patients across all time points (n=144).

Figure 4

Correlation of lean-body mass (LBM) with fat-free mass (FFM) for all patients (Control + Growth Hormone) across different time points (n varies from 40 to 279).

Figure 5

Agreement between lean body mass (LBM; DEXA) and fat-free mass (FFM; K count). The difference between each data pairs is plotted against their mean value (Bland-Altman method). Within the plot, the mean bias between the methods is expressed by the middle line and the upper and lower 95% limits of agreement by the respective upper and lower line. (A) Analysis of all patients, constant limits of agreement. (B) Analysis of all patients, limits of agreement V-shaped around the regression line of the differences (mean bias, equation: y = 0.3506x – 4.7275, R2 = 0.6551). (C) Patients with an average LBM/FFM of 7-17.9 kg. (D) Patients with an average LBM/FFM of 18-65 kg.