Estimating Creatinine Clearance

A Meta-analysis

Sheila M. Wilhelm, Pharm.D.; Pramodini B. Kale-Pradhan, Pharm.D.

Disclosures

Pharmacotherapy. 2011;31(7):658-664. 

In This Article

Abstract and Introduction

Abstract

Study Objectives. To determine which body weight descriptor most accurately predicts measured creatinine clearance (Clcr) and whether rounding serum creatinine concentration (Scr) to 1 mg/dl when it is less than 1 mg/dl accurately predicts measured Clcr.
Design. Meta-analysis of 13 English-language trials comparing 24-hour measured Clcrwith Cockcroft-Gault estimated Clcrby using various body weights or rounded Scr 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 Clcrwere extracted independently by two investigators by using standardized data collection forms. Mean difference (MD) between estimated and measured Clcr 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 Clcr(MD 15.91 ml/min, 95% confidence interval [CI] 7.17–24.65 ml/min). Ideal body weight underestimated Clcr(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 Clcr(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 Clcr (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 Scr value closely estimated measured Clcr (MD 3.51 ml/min, 95% CI −17.18–24.20 ml/min). Ideal body weight with a rounded Scr value underestimated Clcr(MD −29.45 ml/min, 95% CI −48.46 to −10.43).
Conclusion. Using the Cockcroft-Gault equation with no body weight and actual Scr value most closely estimated measured Clcr. In obese patients, it may be reasonable to use actual body weight with a correction factor of 0.3 or 0.4 and actual Scr value in the Cockcroft-Gault equation. Based on this analysis, the use of total body weight, ideal body weight, and a rounded Scr value cannot be recommended.

Introduction

A 24-hour urine collection is required to accurately measure creatinine clearance (Clcr). This is a cumbersome task; therefore, several equations are available for estimating renal function. The Modification of Diet in Renal Disease (MDRD) study equation is used frequently to estimate glomerular filtration rate and aids in the staging of chronic kidney disease;[1–3] however, this equation is not used in determining renally adjusted drug dosages.[4] The Salazar-Corcoran equation has been validated for use in obese patients but is not frequently used in clinical practice.[5] The Cockcroft-Gault equation is routinely used to estimate Clcrand determine proper renal dosing of most drugs.[6] This equation uses a patient's age, serum creatinine concentration (Scr), and weight with an adjustment for females.[7] In the application of the Cockcroft-Gault equation, clinicians use a variety of adjusted variables. Studies have been conducted that used total body weight (TBW), ideal body weight (IBW), adjusted body weight (ABW), and no body weight (NBW).[8–20] For patients with Scr less than 1 mg/dl, some have suggested rounding the Scr value to 1 mg/dl.[8,9,17,19,20] It is unclear whether application of these adjustments allows clinicians to accurately predict Clcr.

The objective of this meta-analysis was to determine which body weight descriptor most accurately predicts measured Clcr. Another objective was to determine whether rounding the Scr value to 1 mg/dl for use in the equation when the Scr is less than 1 mg/dl accurately predicts measured Clcr.

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