Estimating Creatinine Clearance: A Meta-analysis

Abstract

Study Objectives. To determine which body weight descriptor most accurately predicts measured creatinine clearance (Cl_cr) and whether rounding serum creatinine concentration (S_cr) to 1 mg/dl when it is less than 1 mg/dl accurately predicts measured Cl_cr.

Design. Meta-analysis of 13 English-language trials comparing 24-hour measured Cl_cr with Cockcroft-Gault estimated Cl_cr by using various body weights or rounded S_cr values.

Patients. A total of 1197 patients (mean age 53.3 yrs, 48.7% male) were included in the meta-analysis.

Measurements and Main Results. A thorough literature search of the PubMed, MEDLINE, and the Cochrane Library databases was performed (1976-June 2010) to identify relevant clinical trials. Patient population, number of subjects, age, and 24-hour measured and estimated Cl_cr were extracted independently by two investigators by using standardized data collection forms. Mean difference (MD) between estimated and measured Cl_cr was assessed. Thirteen studies met all selection criteria. A random-effects model was applied secondary to a high level of heterogeneity among the studies (I²>50%). Total body weight in the Cockcroft-Gault equation overestimated measured Cl_cr (MD 15.91 ml/min, 95% confidence interval [CI] 7.17–24.65 ml/min). Ideal body weight underestimated Cl_cr (MD −5.15 ml/min, 95% CI −9.92 to −0.38 ml/min). No body weight (i.e., assumes body weight is 72 kg, thus removing the factor of 72 from the denominator of the equation) closely estimated Cl_cr (MD 0.43 ml/min, 95% CI −5.42–6.27 ml/min). Adjusted body weight with correction factors of 0.3 or 0.4 also closely estimated Cl_cr (MD 4.55 ml/min, 95% CI −11.41–20.50 ml/min, and MD 19.94 ml/min, 95% CI −9.6–49.49 ml/min, respectively). Total body weight with a rounded S_cr value closely estimated measured Cl_cr (MD 3.51 ml/min, 95% CI −17.18–24.20 ml/min). Ideal body weight with a rounded S_cr value underestimated Cl_cr (MD −29.45 ml/min, 95% CI −48.46 to −10.43).

Conclusion. Using the Cockcroft-Gault equation with no body weight and actual S_cr value most closely estimated measured Cl_cr. In obese patients, it may be reasonable to use actual body weight with a correction factor of 0.3 or 0.4 and actual S_cr value in the Cockcroft-Gault equation. Based on this analysis, the use of total body weight, ideal body weight, and a rounded S_cr value cannot be recommended.