Abstract
An effective and safe drug therapy for elderly bedridden patients requires an accurate assessment of renal function, since aging affects drug pharmacokinetics in patients. In Japan, based on the enzymatically measured serum creatinine (SCr) value, estimated glomerular filtration rate (eGFR) and estimated creatinine clearance (eCCr) calculated using the Cockcroft-Gault (CG) formula have been used as indicators of patients’ kidney function in routine practice. However, there are some limitations to using eGFR or eCCr directly for elderly patients, because the CG formula is based on data from a non-Japanese population, and uses SCr values measured colorimetrically by the Jaffe method. To overcome these issues, various adjustment protocols for determining the SCr value have been proposed. The purpose of this study was to determine the most accurate adjustment method for SCr values to calculate the eCCr when compared with measured 24-h CCr (mCCr) in elderly bedridden patients.The mCCr was measured by urine collected for 24 h from 45 patients aged 65 years or above, hospitalized at the Naruto Yamakami Hospital between August 2014 and May 2015. The eCCr value was estimated using the CG formula based on SCr value determined by the following methods: (a) actual SCr value by the enzymatic method; (b) + 0.2 correction method, in which the enzymatic SCr value is converted into the Jaffe rate assay; (c) Dooley, in which the SCr value is rounded up to 0.06 mmol/L if below 0.06 mmol/L; (d) Smythe, in which the SCr value is adjusted to 1.0 mg/dL if lower than 1.0 mg/dL; and (e) Furukubo, in which the SCr value is adjusted to 0.8 mg/dL if lower than 0.8 mg/dL in males and to 0.6 mg/dL if lower than 0.6 mg/dL in females.Comparison of mCCr (control group) with the eCCr of each group by the Dunnett test revealed a significant difference between them in the (a) and (d) groups (p < 0.05). Bland-Altman analysis showed a consistency in eCCr and mCCr values in groups (b), (c), and (e). Finally, comparison of prediction accuracy as a percentage of patients with eCCr values within ±30% of mCCr values showed that group (b) had the highest accuracy at 75.6%, followed by group (c) at 71.1%.A comparison of mCCr and eCCr values obtained by different methods showed that consistency between eCCr and mCCr was greatest when the SCr value was adjusted by the + 0.2 correction method, adding 0.2 mg/dL to the enzymatically measured SCr value.
