Evaluation of a creatinine clearance correction equation based on body fat mass in older Japanese patients with diabetes.

Background: The estimation of creatinine clearance (CCr) in older adult patients with diabetes is subject to deviations from the results of actual measurements because of changes in body composition. In the present study, we aimed to create a correction for the equation used for the estimation of CCr in older adult Asian patients with diabetes using body composition parameters. Methods: We enrolled 50 older Japanese patients with diabetes in whom the measured values of CCr were compared with values estimated using the Cockcroft-Gault equation. The relationships between the error in the estimated CCr and body composition parameters were investigated, and the Cockcroft-Gault equation was corrected using the appropriate parameters. To evaluate the generalizability of the corrected equation, the utility of the Cockcroft-Gault equation, which was corrected on the basis of body composition measured using a household body composition meter, was also investigated. Results: Body fat mass (BFM) was closely correlated with the error in the estimated CCr. The BFM-corrected Cockcroft-Gault equation was more accurate than the original equation. Similarly, the error became smaller using BFM measured with a household body composition meter. Conclusion: The BFM-corrected Cockcroft-Gault equation may provide an accurate method of estimating CCr that can be used in general practice.

Investigation of methods for more accurate estimation of kidney function in people with high muscle mass
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Serum creatinine (SCr) levels depend on muscle mass and are therefore elevated in people with high muscle mass, potentially leading to underestimation of kidney function in this population. Although recent therapeutic guidelines have shown measurement of serum cystatin C (ScysC) to be useful, this method has not been validated in people with high muscle mass. We conducted this study to investigate methods for more accurately estimating kidney function in people with high muscle mass. Linear regression analysis was used to assess the correlation of endogenous creatinine clearance (24-hour CLcr) and 24-hour CLcr × 0.715 (i.e., modified glomerular filtration rate (GFR)); with estimated kidney function from SCr and ScysC in 15 healthy young adult men with high muscle mass. A significant but weak positive correlation was observed between 24-hour CLcr and estimated CLcr by the Cockcroft and Gault formula (CG CLcr; R2 = 0.371, p = 0.016). The estimated GFR calculated from ScysC (eGFRcys) was significantly higher than CLcr × 0.715, but the two were not correlated (R2 = 0.125, p = 0.197). However, when CG CLcr and eGFRcr were adjusted by muscle mass parameters, the correlation between measured and estimated values improved. Further improvement was seen when participants with a fat mass greater than 25% were excluded (R2 = 0.623, p = 0.004; R2 = 0.510, p = 0.014; n = 11 for both). The results of our study suggest that currently used formulas for estimating kidney function, including eGFRcys, may not be appropriate for people with high muscle mass, but use of muscle mass parameters may improve predictivity.
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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.

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 (R2) 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 R2 (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 R2 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 R2 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 R2 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.