Modified serum creatinine-derived equations with muscle mass-adjusted estimation of renal function and serum cystatin C-derived estimated glomerular filtration rate in elderly individuals
.

Aims: Serum creatinine (Cr)-derived estimated renal function indices are overestimated in elderly patients with reduced muscle mass (MM). We sought to identify equations correlated with measured glomerular filtration rate (mGFR) and assess the effect of bioelectrical impedance analysis (BIA)- or arm muscle circumference (AMC)-determined MM on performance.
Materials and Methods: This study involved 20 elderly patients aged 76.0 ± 6.8 (65 - 85) years, including 5 bedridden patients. Serum Cr, Cr clearance (CCr), and cystatin C (CysC) were measured, and correlations with estimated renal indices were investigated. We also assessed if BIA- or AMC-determined MM in such equations improved performance.
Results: Measured CCr (mCCr) × 0.715 was regarded as mGFR, which was correlated with estimated GFR (eGFRcr), more strongly after excluding bedridden patients (R = 0.393, n = 20; R = 0.925, respectively, when n = 15). Correlation between mGFR and eGFRcys in 20 cases (R = 0.894, p < 0.0001) was the most accurately quantified renal function in bedridden patients. In ambulatory cases, correlation was strong between mGFR and eGFR with use of BIA-determined MM in the eGFRcr equation (R = 0.904, p < 0.0001; n = 15).
Conclusion: eGFR derived from equations with MM-for-body-weight substitution, and eGFRcys independent of MM, may be a more exact measure of renal function than conventional serum Cr-derived estimates in elderly bedridden patients.
.