Estimation of Creatinine Clearance in Morbidly Obese Patients

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

Disclosures

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

In This Article

Results

A total of 58 patients were recruited and completed study procedures; however, the urine samples of 4 patients were lost, who were thus excluded. Table 1 summarizes the demographics of the 54 study patients, the majority of whom were women (63%). The race and ethnicity of the study population were consistent with demographic features of New Mexico. Forty-six patients (85%) had an SCr concentration of ≤1.0 mg/dL, and only 2 (4%) had an SCr concentration over 1.4 mg/dL. Seventeen patients (31%) had a BMI of ≥50 kg/m2. The various body-size descriptors provided weight measures that were 34.3-57.3% lower than the TBW. The mean ± S.D. values of these body-size descriptors were as follows: 60.8 ± 11.2 kg for IBW, 85.3 ± 17.4 kg for ABW0.3, 93.4 ± 20.6 kg for ABW0.4, 72.1 ± 19.6 kg for FFW, and 66.8 ± 14.8 kg for LBW.

The mean ± S.D. measured CLcr was 109.5 ± 44.4 mL/min. The mean, bias, precision, and accuracy of the various estimation methods are summarized in Table 2. Only the Cockcroft-GaultFFW and Cockcroft-GaultLBW provided estimates of CLcr that were not significantly different (p > 0.05) from measured values. In addition, both of these equations provided unbiased estimates of measured CLcr (Figure 1). As expected, use of Cockcroft-GaultTBW grossly overestimated measured CLcr. The Cockcroft-GaultABW0.3, Cockcroft-GaultABW0.4, and Salazar-Corcoran equations all overestimated measured CLcr values in the study patients. In contrast, the Cockcroft-GaultIBW and the MDRD4 equations underestimated measured CLcr values. The Cockcroft-GaultLBW equation was the most precise, and the MDRD4 equation was the least. The Cockcroft-GaultFFW and Cockcroft- GaultLBW equations yielded the highest accuracy (55-61%), in yielding values that were within 30% of the measured CLcr.

Figure 1.

Bland-Altman plots of measured 24-hour creatinine clearance (CLcr) versus CLcr estimated by the Cockcroft-Gault (CG) method using total body weight (TBW) (A), ideal body weight (IBW) (B), adjusted body weight with constant 0.3 (ABW0.3) (C), ABW with constant 0.4 (ABW0.4) (D), fat-free weight (FFW) (E), and lean body weight (LBW) (F). The dashed line represents the interval mean of 1.96 S.D. to -1.96 S.D.

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