Coefficient of Determination between Estimated and Measured Renal Function in Japanese Patients with Sarcopenia May Be Improved by Adjusting for Muscle Mass and Sex: A Prospective Study

Abstract

Creatinine (Cr) levels are strongly affected by muscle mass, and the estimated glomerular filtration rate (eGFR), a measure based on serum creatinine (SCr), is often overestimated in patients with sarcopenia. To evaluate the coefficient of determination (R 2) between eGFR and the actual measured value, we performed a linear regression analysis of a modified GFR (mGFR: measured Cr clearance 0.715) and various renal function estimates adjusted for muscle mass in 19 patients with sarcopenia. The eGFR values based on SCr (eGFRcr) were higher than those based on mGFR, although a high R 2 (0.704; p < 0.001) was found between these values. There was no deviation between eGFR based on serum cystatin C (eGFRcys) and mGFR, although the R 2 value 0.691 was equivalent to that of eGFRcr. In the equation used to calculate eGFRcr not adjusted for body surface area (mL/min), muscle mass parameters obtained from bioelectrical impedance analysis were used instead of actual body weight to recalculate the eGFRcr. The R 2 between this eGFRcr and mGFR did not improve, although there was less deviation. However, assuming that all patients were female by using female coefficients for all patients, the R 2 between eGFRcr-fcc (eGFRcr with female coefficient correction) and mGFR improved and was the highest (0.808) on substitution of appendicular skeletal muscle mass. The correlation between eGFRcr-fcc and mGFR improved over eGFRcys when muscle mass was substituted for body weight in the equation used to estimate eGFR in patients with sarcopenia and sex differences were removed.

Prediction Accuracy of Area under the Concentration–Time Curve of Vancomycin by Bayesian Approach Using Creatinine-Based Equations of Estimated Kidney Function in Bedridden Elderly Japanese Patients

“…However, SCr level is strongly affected by muscle mass, leading to overestimation of kidney function in elderly sarcopenic patients. 10) In this study, there was a significant correlation between AUC REF and AUC eGFR/0.789 (p < 0.001) where AUC eGFR/0.789 tended to be lower in relation to AUC REF (Fig. 1).…”

“…Therefore, we recommend against using eGFR/0.789 equations while planning the administration of VCM in such patients. Nakatani et al 10) reported that the prediction accuracy of kidney function could be improved by considering the muscle mass in the eGFR equation. Accordingly, further studies are needed to determine whether the Bayesian approach using the eGFR/0.789, which considers muscle mass, can improve the prediction accuracy for the AUC.…”

“…Furthermore, assessing kidney function using cystatin C is effective in patients with conditions in which muscle mass is reduced, such as sarcopenia. 10) However, cystatin C is affected by thyroid function and some drugs, including steroids and cyclosporine. 11,12) It is also expensive to measure and is only permitted once every three months in the Japanese health insurance system.…”

“…On the other hand, SCr is frequently used as an indicator of kidney function in clinical practice, 13) and is inexpensive to determine. However, it is difficult to accurately evaluate kidney function in patients with decreased muscle mass, such as bedridden elderly patients, 10) because their SCr concentrations remain the same; thus, resolving this issue would be very clinically beneficial. Otani et al 14) reported that consistency between estimated creatinine clearance (eCCr) and measured CCr was highest when the SCr level was adjusted by adding 0.2 mg/dL to the enzymatically measured SCr value in bedridden elderly patients.…”

“…However, there are few studies on the prediction accuracy of the AUC of VCM by the Bayesian approach using creatinine-based equations of estimated kidney function in such patients. The estimated kidney function using SCr tends to be overestimated in bedridden elderly patients, 10) leading to an overdose of VCM. Thus, there is an urgent need to establish an administration plan for VCM in such patients.…”