An analysis of measured and estimated creatinine clearance rates in normal weight, overweight, and obese patients with gynecologic cancers.

STUDY
OBJECTIVE: Different equations used to estimate creatinine clearance (Cl(cr)) in obese oncology patients can produce divergent estimated creatinine clearance values, which in turn can result in significantly different calculated carboplatin doses. Standardization of the calculation of creatinine clearance in patients of all body types is a desirable goal. The objective of our study was to examine the impact of increasing body mass index on the accuracy of creatinine clearance estimation methods and to determine the optimal equation for creatinine clearance estimation in the obese adult female cancer patient.
DESIGN: Retrospective data analysis. PATIENTS: We compared the estimated creatinine clearance values produced by each of 11 equations to 24-hour creatinine clearance values measured in 119 adult female patients with gynecologic cancers grouped according to body composition.
MEASUREMENTS AND MAIN RESULTS: We applied simple linear regression and Tukey mean-difference analysis to assess the relationship between estimated creatinine clearance values produced by these equations and measured creatinine clearance values for each patient. The relationship between measured creatinine clearance and estimated creatinine clearance produced by all equations displayed lower linear regression R (2) values and higher limits of agreement in obese patients than in nonobese groups. Agreement between measured and estimated creatinine clearance produced by the Cockcroft-Gault equation is sensitive to the particular weight parameter incorporated and is lowest using ideal weight or actual body weight. The Cockcroft-Gault equation incorporating an intermediate weight value reduced estimation bias. The Jelliffe equation produced the lowest R (2) values.
CONCLUSION: Available model equations are less reliable for predicting creatinine clearance in obese female cancer patients (body mass index >30) than in nonobese patients. A measured glomerular filtration rate or creatinine clearance value is most accurate in obese female cancer patients. When using Cockcroft-Gault equation for estimation in this patient population, however, an intermediate weight value (adjusted or modified-adjusted) rather than ideal or actual body weight should be used.