Estimation of Creatinine Clearance in Morbidly Obese Patients

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 ABW_0.3, 93.4 ± 20.6 kg for ABW_0.4, 72.1 ± 19.6 kg for FFW, and 66.8 ± 14.8 kg for LBW.

The mean ± S.D. measured CL_cr 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-Gault_FFW and Cockcroft-Gault_LBW provided estimates of CL_cr that were not significantly different (p > 0.05) from measured values. In addition, both of these equations provided unbiased estimates of measured CL_cr (Figure 1). As expected, use of Cockcroft-Gault_TBW grossly overestimated measured CL_cr. The Cockcroft-GaultABW_0.3, Cockcroft-GaultABW_0.4, and Salazar-Corcoran equations all overestimated measured CL_cr values in the study patients. In contrast, the Cockcroft-Gault_IBW and the MDRD4 equations underestimated measured CL_cr values. The Cockcroft-Gault_LBW equation was the most precise, and the MDRD4 equation was the least. The Cockcroft-Gault_FFW and Cockcroft- Gault_LBW equations yielded the highest accuracy (55-61%), in yielding values that were within 30% of the measured CL_cr.

(Enlarge Image)

Figure 1.

Bland-Altman plots of measured 24-hour creatinine clearance (CL_cr) versus CL_cr 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 (ABW_0.3) (C), ABW with constant 0.4 (ABW_0.4) (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.

Cite this: Estimation of Creatinine Clearance in Morbidly Obese Patients - Medscape - Mar 31, 2009.

Table 1. Patient Characteristics
Variable	Women (n = 34)	Men (n = 20)	Total (n = 54)
Age (yr)
Mean ± S.D.	51.3 ± 12.5	43.6 ± 12.4	48.4 ± 12.9
Median (range)	52.0 (29.0-74.0)	47.5 (21.0-65.0)	48.5 (21.0-74.0)
Race/ethnicity (no. [%])
Non-Hispanic white	18 (53)	9 (45)	27 (50)
Hispanic	14 (41)	9 (45)	23 (43)
Native American	1 (3)	2 (10)	3 (6)
Black	1 (3)	0	1 (2)
Serum creatinine concentration (mg/dL)
Mean ± S.D.	0.8 ± 0.3	0.9 ± 0.2	0.8 ± 0.3
Median (range)	0.7 (0.5-1.8)	0.8 (0.6-1.3)	0.8 (0.5-1.8)
Total body weight (kg)
Mean ± S.D.	132.7 ± 35.0	158.7 ± 47.6	142.3 ± 41.7
Median (range)	123.8 (99.0-256.0)	147.0 (112.0-320.0)	128.2 (99.0-320.0)
Body mass index (kg/m²)
Mean ± S.D.	50.6 ± 12.0	50.3 ± 13.9	50.5 ± 12.6
Median (range)	45.6 (40.1-88.6)	45.2 (40.2-95.6)	45.6 (40.1-95.6)

Table 2. Performance of Various Methods of Estimating Creatinine Clearance (CL _cr) or Glomerular Filtration Rate (GFR) ^a
Method	Mean ± S.D. or GFR CL_cr (mL/min)	Mean Bias (mL/min) (95% CI)	Precision		Accuracy (% Patients)
Method	Mean ± S.D. or GFR CL_cr (mL/min)	Mean Bias (mL/min) (95% CI)	r ²	RMSE	≤30% of Measured CL_cr	≤50% of Measured CL_cr
Measured CL_cr	109.5 ± 44.4
Cockcroft-Gault_TBW	216.9 ± 113.1	-107.4 (-133.2, -81.5)	0.272	37.83	12.9	29.6
Cockcroft-Gault_IBW	85.3 ± 29.4	24.3 (14.6, 33.9)	0.326	36.41	48.1	88.9
Cockcroft-Gault ABW_0.3	129.4 ± 55.3	-19.8 (-32.1, -7.6)	0.339	36.07	53.7	75.9
Cockcroft-Gault ABW_0.4	141.9 ± 63.1	-32.3 (-46.2, -18.5)	0.326	36.40	51.8	66.7
Cockcroft-Gault_FFW	102.7 ± 48.1	6.8 (-4.5, 18.2)	0.324	36.46	61.1	83.3
Cockcroft-Gault_LBW	101.5 ± 43.3	8.1 (-2.6, 18.7)	0.352	35.68	55.6	87.0
Salazar-corcoran	155.2 ± 65.1	-45.7 (-59.9, -31.5)	0.326	36.40	46.2	55.6
MDRD4	96.3 ± 29.4	13.3 (2.3, 24.3)	0.172	40.36	51.9	87.0

^aCI = confidence interval; RMSE = root mean-squared error; TBW = total body weight; IBW = ideal body weight; ABW_0.3 = adjusted body weight (ABW) using 0.3 to represent gain in lean body weight (LBW) between TBW and IBW; ABW_0.4 = ABW using 0.4 to represent gain in LBW between TBW and IBW; FFW = fat-free weight; MDRD4 = four-variable Modification of Diet in Renal Disease equation.

Commenting is limited to medical professionals. To comment please Log-in.

Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.

My Alerts

Add to Email Alerts

Your Name is required.

Subject is required.

Please enter a Recipient Address and/or check the Send me a copy checkbox.

Your email has been sent.

is an Invalid Email Address.

Estimation of Creatinine Clearance in Morbidly Obese Patients

Results

Tables

Tables

References

Authors and Disclosures

Authors and Disclosures

Appendix

Appendix: Equations and Body Weights Used in Study

Figure 1.

Figure 1.

Comments

Email This

Feedback