Effects of Body Composition on Renal Function Estimates in Older Patients

The modified Cockcroft-Gault (CG) equation, previously developed for an aged-oriented cohort, was validated in a newly obtained dataset. Estimates of creatinine clearance (CCr) using this equation were found to be more accurate than those determined using the conventional CG equation, particularly for patients exceeding 65 years of age. We identified a subset of patients in this cohort whose estimates were inadequate. Using statistical analysis, we found that the deviation from estimates was attributed to a decreased albumin level. In addition, we determined a reduced albumin cutoff value for the modified CG equation to obtain a good estimate. Univariate linear regression analysis was applied to measure the CCr in this cohort and identify parameters related to body composition, and we found that extracellular water (ECW)/total body water (TBW) and body fat (%) were relevant. Using measured values of ECW/TBW and body fat (%), a multivariate linear regression (MLR) estimating equation was developed based on the modified CG equation. This equation was applied to a cohort over 65 years of age, and it was found that a good estimate was obtained for older patients with low albumin levels. Thus, we propose a flow diagram that illustrates conditions for selecting an appropriate estimating equation from among the CG, modified CG, and MLR equations.