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Probability of Reduced Renal Function After Contrast-Enhanced CT: A Model Based on Serum Creatinine Level, Patient Age, and Estimated Glomerular Filtration Rate

¹ Imaging Institute, Cleveland Clinic, 9500 Euclid Ave., Desk Hb6, Cleveland, OH 44195.
² Department of Quantitative Health Sciences, Cleveland Clinic, Cleveland, OH.
³ Department of Nephrology and Hypertension, Glickman Urological and Kidney Institute, Cleveland Clinic, Cleveland, OH.
⁴ Department of Internal Medicine, Cleveland Clinic, Cleveland, OH.

OBJECTIVE. The objectives of our study were to develop a model to predict the probability of reduced renal function after outpatient contrast-enhanced CT (CECT)—based on patient age, sex, and race and on serum creatinine level before CT or directly based on estimated glomerular filtration rate (GFR) before CT—and to determine the relationship between patients with changes in creatinine level that characterize contrast-induced nephropathy and patients with reduced GFR after CECT.

MATERIALS AND METHODS. Of 5,187 outpatients who underwent CECT, 963 (18.6%) had serum creatinine levels obtained within 6 months before and 4 days after CECT. The estimated GFR was calculated before and after CT using the four-variable Modification of Diet in Renal Disease (MDRD) Study equation. Pre-CT serum creatinine level, age, race, sex, and pre-CT estimated GFR were tested using multiple-variable logistic regression models to determine the probability of having an estimated GFR of < 60 and < 45 mL/min/1.73 m² after CECT. Two thirds of the patients were used to create and one third to test the models. We also determined discordance between patients who met standard definitions of contrast-induced nephropathy and those with a reduced estimated GFR after CECT.

RESULTS. Significant (p < 0.002) predictors for a post-CT estimated GFR of < 60 mL/min/1.73 m² were age, race, sex, pre-CT serum creatinine level, and pre-CT estimated GFR. Sex, serum creatinine level, and pre-CT estimated GFR were significant factors (p < 0.001) for predicting a post-CT estimated GFR of < 45 mL/min/1.73 m². The probability is [exp(y) / (1 + exp(y))], where y = 6.21 - (0.10 x pre-CT estimated GFR) for an estimated GFR of < 60 mL/min/1.73 m², and y = 3.66 - (0.087 x pre-CT estimated GFR) for an estimated GFR of < 45 mL/min/1.73 m². A discrepancy between those who met contrast-induced nephropathy criteria by creatinine changes and those with a post-CT estimated GFR of < 60 mL/min/1.73 m² was detected in 208 of the 963 patients (21.6%).

CONCLUSION. The probability of a reduced estimated GFR after CECT can be predicted by the pre-CT estimated GFR using the four-variable MDRD equation. Furthermore, standard criteria for contrast-induced nephropathy are poor predictors of poor renal function after CECT. Criteria need to be established for what is an acceptable risk to manage patients undergoing CECT.

Keywords: contrast-enhanced CT • contrast-induced nephropathy • estimated glomerular filtration rate • IV contrast material • Modification of Diet in Renal Disease (MDRD) equation • renal function

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