Estimation of Creatinine Clearance in Morbidly Obese Patients

Jasmina A. Demirovic; Amy Barton Pai; Manjunath P. Pai


Am J Health Syst Pharm. 2009;66(7):642-648. 

In This Article

Abstract and Introduction


Purpose: Estimates of creatinine clearance (CLcr) based on equations and various body-size descriptors were compared with 24-hour measured CLcr values in morbidly obese patients.
Methods: Patients age 18-75 years with a body mass index (BMI) of ≥40 kg/m2 with stable serum creatinine values were enrolled. Covariates known to contribute to alteration in CLcr were used to exclude patients. Twenty-four-hour urine collection was performed to measure CLcr. Bioelectric impedance analysis was used to estimate fat-free weight (FFW). Glomerular filtration rate was estimated using the four-variable Modification of Diet in Renal Disease (MDRD4) equation. CLcr was estimated using the Cockcroft-Gault and Salazar-Corcoran methods using total body weight (TBW). Body-size descriptors, such as ideal body weight (IBW), adjusted body weight (ABW), and lean body weight (LBW), and FFW were substituted in the Cockcroft-Gault equation to generate additional estimates of CLcr.
Results: Fifty-four patients (mean ± S.D. age, 48.4 ± 12.9 years; TBW, 142.3 ± 41.7 kg; BMI, 50.5 ± 12.6 kg/m2) completed the study. All three equations were biased in their estimation of CLcr. Use of MDRD4 and IBW in the Cockcroft-Gault equation underestimated CLcr, while the Salazar-Corcoran equation and use of TBW or ABW in the Cockcroft-Gault equation overestimated this value. Substitution of fat-free weight or LBW in the Cockcroft-Gault equation provided unbiased estimates of CLcr.
Conclusion: An LBW estimate, based on TBW and BMI, incorporated into the Cockcroft-Gault equation provided an unbiased, relatively precise, accurate, and clinically practical estimate of 24-hour measured CLcr in morbidly obese patients.


Accurate estimation of renal function is particularly problematic in morbidly obese patients. We compared estimates of creatinine clearance (CLcr) that used various body-size descriptors to determine which method most closely approximated the actual measured 24-hour CLcr in morbidly obese patients.


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