BODY-COMPOSITION MEASUREMENT IN 9-11-Y-OLD CHILDREN BY DUAL-ENERGY X-RAY ABSORPTIOMETRY, SKINFOLD-THICKNESS MEASUREMENTS, AND BIOIMPEDANCE ANALYSIS

We compared, in 9-11-y-old children (n = 43), three measures of body c omposition: dual-energy X-ray absorptiometry (DXA), skinfold thickness , and bioimpedance analysis (BIA). The intraclass correlation coeffici ent (ICC), Bland-Altman procedure, and Spearman rank correlation were used to determine test-retest reliabilities of the three methods and t o compare methods. For DXA measurements, the rank correlation between fat-free soft tissue acid fat-free mass (FFM) was > 0.99, indicating t hat bone mineral content did not provide independent information. Thus , subsequent analyses used the two-compartment model tie, fat mass and FFM) for all three techniques, focusing especially on ;I values for p ercentage of fat. The test-retest reliabilities for all methods were h igh (ICCs > 0.994 and no significant differences between trials 1 and 2). The range of individual differences from I: trial 1 to trial 2 and Bland-Altman limits of agreement suggested that the reliability was g reatest for DXA, followed by BIA and skinfold-thickness measurement. T he percentage of fat values for the three methods were highly intercor related (all Spearman r values > 0.83). However, there was a systemati c tendency (P < 0.01) for DXA values (mean: 23.98) to be higher than t hose derived from skinfold-thickness measurements (mean: 21.05) and BI A (mean: 21.52). The variance in percentage of fat values for BIA was significantly smaller than that for the other two techniques. These fi ndings, along with rather large limits of agreement derived from the B land-Altman procedure, suggest that the methods should not be used int erchangeably.