Measured versus estimated creatinine clearance in elderly patients

Abstract

The accuracy of five equations that estimate creatinine clearance (Clcr) have been assessed and the influence of bodyweight types and rounding serum creatinine (SCr) to 1 mg/dL evaluated in elderly patients. Sixty-four elderly patients (35 male: 54.7%) who had a stable SCr level in general medical wards at Ramathibodi Hospital, Thailand were recruited. The estimated Clcr values were compared with measured Clcr by predictive performance statistics. The former were calculated from five equations; Jelliffe's, Mawer's Cockcroft & Gault's, Bjornsson's and Hull's equations, using actual, ideal, and adjusted body weights and rounding SCr values to 1 mg/dL whereas the latter were calculated from 24-hour urine samples. The average age of the study group was 70.9 ± 7.5 years old with a mean SCr value of 1.12 ± 0.54 mg/dL. An average measured Clcr was 42.21 ± 17.06 mL/min. The biases and precisions of Mawer's equation using actual body weight, ideal body weight, Hull's equation using adjusted body weight, and Cockcroft and Gualt's equation using adjusted body weight were 1.79, [95%CI,-2.73,6.30] & 18.00; 2.63, [95%CI,-2.05,7.30] & 18.77; -3.37, [95%CI,-7.90,1.16] & 18.31; and -4.06, [95%CI,-8.52,0.04] & 18.16 mL/min, respectively. All of these estimated Clcr were unbiased and provided the most precise value. An average measured Clcr was 47.14 ± 20.32 mL/min in the 24 elderly patients with SCr less than 1 mg/dL. The Bjornsson's equation using actual body weight was the best equation when rounding SCr to 1 mg/dL (bias, 1.65; [95%CI,-5.80, 9.10] & precision, 17.35 mL/min) comparing with actual SCr (bias, -20.39; [95%CI,-30.19, -10.59] & precision, 30.96 mL/min). The Mawer's equation using actual body weight should be suggested to predict Clcr. Rounding SCr to 1 mg/dL is suggested to estimate Clcr in patients who have SCr less than 1 mg/dL.