COMPARISON OF MEASUREMENTS OF BODY-COMPOSITION BY TOTAL-BODY POTASSIUM, BIOIMPEDANCE ANALYSIS, AND DUAL-ENERGY X-RAY ABSORPTIOMETRY IN HYPOPITUITARY ADULTS BEFORE AND DURING GROWTH-HORMONE TREATMENT

We compared fat-free mass (FFM) and percentage body fat mass (BFM) val ues derived from total body potassium (TBK), bioelectrical impedance a nalysis (BIA), and dual-energy X-ray absorptiometry (DXA) in hypopitui tary adults before and after 6 mo treatment with growth hormone. Befor e growth hormone treatment, FFM values from the three methods correlat ed strongly. FFM values from TBK were lower than FFM values derived fr om BIA and DXA (($) over bar x +/- SD: 53.7 +/- 14.3 compared with 49. 1 +/- 9.2 kg, P < 0.0001; DXA compared with TBK: 54.7 +/- 16.4 and 49. 2 +/- 9.7 kg, P < 0.0002). BFM values from TBK were significantly high er than the BIA-derived (P < 0.002) but not different from the DXA-der ived values. There was no difference in FFM and BFM values derived fro m DXA and BIA methods. The differences between BLA and TBK methods and between DXA and TBK methods were observed in the obese but not in the nonobese subjects. The increase in FFM derived from BLA with growth h ormone was greater than that derived from TBK ([median(range)]; BIA: 5.2(-0.1, +13.8) compared with TBK: +0.9(-4.8, +8.6) kg, P < 0.001, bu t the changes with placebo were not different. The changes in FFM and BFM derived from DXA with growth hormone and placebo were not signific antly different from those derived by using TBK or BIA. We conclude th at FFM and BFM values derived from TBK, BIA, and DXA correlate highly and that TBK-derived values for FFM are lower than those derived from BIA and DXA in obese patients.