Comparison of total body potassium with other techniques for measuring lean body mass in men and women with AIDS wasting

Background: Lean body mass is an important predictor of survival and functi onal status in patients with AIDS wasting. The bias between different techn iques for assessing body composition in AIDS wasting is not known. Design: We compared total body potassium (TBK) with fat-free mass (FFM) det ermined by dual-energy X-ray absorptiometry (DXA), bioelectrical impedance analysis (BIA), and skinfold-thickness measurement (SKF) in 132 patients (6 3 men, 69 women) with AIDS wasting (weight < 90% of ideal body weight, or w eight loss > 10% of original, or both). None of the subjects exhibited clin ical lipodystrophy. Comparisons were made by using different BIA equations. Results: Lean body mass determined by DXA was highly correlated with TBK in men (r = 0.79, P < 0.0001) and women (r = 0.84, P < 0.0001). FFMBIA and FF MDXA were significantly different (P < 0.01 in men and P < 0.0001 in women) . The difference between FFMDXA and FFMBIA was significantly greater with g reater weight and body fat, particularly in HIV-infected women (r = -0.39, P = 0.001 for weight; r = -0.60, P < 0.0001 for fat). The comparability of FFM and fat mass determined by DXA and BIA was dependent on the specific BI A equation used. Among men, no single BIA equation was more highly predicti ve of fat mass and FFM in comparison with DXA. Conclusions: The differences between DXA, BIA, and SKF in the determination of fat mass and FFM are significant in patients with AIDS wasting, BIA ove restimates FFM compared with DXA in those with greater body fat. Standard B IA equations may not accurately estimate FFM and fat mass in men and women with AIDS wasting.