Estimation of lean body weight in older women with hip fracture

Objective

Lean body weight (LBW) decreases with age while total body fat increases, resulting in altered drug pharmacokinetics. A semi-mechanistic equation estimating LBW using height, weight and sex has been developed for potential use across a wide range of body compositions. The aim of this study was to determine the ability of the LBW equation to estimate dual energy x-ray absorptiometry-derived fat free mass (FFM_DXA) in a population of older women with recent hip fracture.

Methods

Baseline, four and 12 month data obtained from 23 women enrolled in the Sarcopenia and Hip Fracture study were pooled to give 58 measurements. LBW was estimated using the equation: $LBW(kg) = frac{{9270 times Wt}} {{8780 + (244 times BMI)}} $ Body composition was classified as: ??normal?? (BMI <25kg/m² and not sarcopenic), ??overweight-obese?? (BMI >25kg/m² and not sarcopenic), ??sarcopenic?? (sarcopenic and BMI <25kg/m²), or ??sarcopenic-obese?? (sarcopenic and BMI >25kg/m²). The ability of the LBW equation to predict FFM_DXA was determined graphically using Bland-Altman plots and quantitatively using the method of Sheiner and Beal.

Results

The mean ± SD age of female participants women was 83±7 years (n=23). Sarcopenia was frequently observed (65.2%). Bland-Altman plots demonstrated an underestimation by the LBW equation compared to FFM_DXA. The bias (95% CI) and precision (95% CI) calculated using the method of Sheiner and Beal was 0.5kg (?0.7, 1.66kg) and 4.4kg (?3.7, 12.4kg) respectively for pooled data.

Conclusion

This equation can be used to easily calculate LBW. When compared to FFM_DXA, the LBW equation resulted in a small underestimation on average in this population of women with recent hip fracture. The degree of bias may not be clinically important although further studies of larger heterogeneous cohorts are needed to investigate and potentially improve the accuracy of this predictive equation in larger clinical cohorts.