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Identifying Outpatients with Renal Insufficiency before Contrast-enhanced CT by Using Estimated Glomerular Filtration Rates versus Serum Creatinine Levels¹

¹ From the Division of Radiology (B.R.H., M.E.B., E.S.), Department of Nephrology and Hypertension (E.D.P.), and Department of Quantitative Health Sciences (N.A.O.), Cleveland Clinic, 9500 Euclid Ave, Desk Hb6, Cleveland, OH 44195. Received August 29, 2007; revision requested October 29; revision received November 17; accepted January 8, 2008; final version accepted February 19. Supported in part by a research award from the Society of Computed Body Tomography. Address correspondence to B.R.H. (e-mail: hertsb@ccf.org).

Purpose: To determine whether using estimated glomerular filtration rate (eGFR) values rather than serum creatinine levels to identify patients with renal insufficiency facilitates any substantial change in the number of outpatients scheduled for computed tomography (CT) who are considered at increased risk for contrast medium–induced nephropathy.

Materials and Methods: The study was HIPAA compliant and institutional review board approved for medical chart review; the requirement for informed patient consent was waived. Patients (n = 5138; 2569 women, 2569 men, 753 African Americans, 4385 non–African Americans) examined during a 2-year period formed the final study group after exclusion of patients undergoing dialysis (n = 49), for whom no age data were recorded (n = 9), and younger than 18 years (n = 113). Patient age, sex, and race and the blood urea nitrogen, albumin, and serum creatinine levels most recently measured within 6 months before CT were obtained from the electronic medical records. The number of patients with creatinine levels higher than 1.4 mg/dL was directly compared with the number of patients with eGFR values (calculated with four- and six-variable Modification of Diet in Renal Disease [MDRD] equations) lower than 60 mL/min/1.73 m² by using the two-tailed McNemar test. For 2689 patients, data to calculate the eGFR by using the four-variable equation were available, and for 2005 patients, data to calculate the eGFR by using the six-variable equation were available.

Results: Among the outpatients scheduled to undergo CT, the percentage of patients with an eGFR lower than 60 mL/min/1.73 m² was significantly greater than the percentage of patients with a creatinine level higher than 1.4 mg/dL for both the four-variable (412 [15.3%] vs 166 [6.2%] of 2689 patients) and the six-variable (346 [17.3%] vs 117 [5.8%] of 2005 patients) MDRD equation groups (P < .001).

Conclusion: A significantly higher number of outpatients scheduled for contrast medium–enhanced CT met the National Kidney Foundation criteria for renal insufficiency when the MDRD equations were used to estimate the glomerular filtration rate compared with the number of outpatients who met the criteria on the basis of elevated creatinine levels.

© RSNA, 2008

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