Figure 1. CT scan demonstrating contrast induced nephropathy - A CT without contrast administration in a patient who had undergone a contrast-enhanced CT scan followed by coronary catheter angiography three days before demonstrates retention of iodinated contrast in the renal cortices bilaterally (arrows). Serum creatinine values increased from a baseline of 1.6 to 3.2 at the time of this CT exam.

Table 1. Predisposing factors for the development of contrast-induced nephropathy with CT examination

Coexisting medical/demographic factors: - Renal insufficiency - Diabetes - Congestive heart failure - Dehydration - Age > 75 yrs - Multiple myeloma

Concurrent use of potentially nephrotoxic medications: - Non-steroidal anti-inflammatory agents (NSAIDS) - Cisplatin-based chemotherapy agents - Aminoglycoside antibiotics - Iodinated contrast within last 72 hours

Although high serum creatinine levels have traditionally been regarded as an indicator of renal insufficiency, it is now recognized that creatinine levels in isolation are a poor measure of renal function as they vary with muscle mass Therefore, current recommendations are that the estimated glomerular filtration rate (eGFR), as calculated using the Modification of Diet in Renal Disease (MDRD) equation, be used to determinate baseline renal function.  The MDRD eGFR equation requires inputs of serum creatinine, patient age, and race as follows:

GFR (mL/min/1.73 m²) = 186 x (Serum
Creatinine)^-1.154 x (Age)^-0.203 x (0.742 if female) x (1.210 if African American)

eGFR is now often provided along with serum creatinine by hospital chemistry laboratories. If unreported, eGFR calculators can readily be found on the Internet, are available for personal digital assistants, and as handheld plastic quick reference pocket cards.

Thus, prior to a patient undergoing contrast-enhanced CT study, a comprehensive medical history must be obtained to identify any predisposing factors for CIN (Figure 2). Patients with risk factors will require a serum creatinine level to calculate the eGFR prior to the study.

Figure 2.  Guidelines for risk stratification and prophylaxis for CIN
	High Risk	Intermediate Risk	Low Risk
	Estimated GFR < 30 mL/min/1.73 m2	Estimated GFR 30-60 mL/min/1.73 m2	Estimated GFR > 60 mL/min/1.73 m2
Contrast Administration	Avoid contrast*	Administer contrast	Administer contrast
Oral Hydration	N/A	Encouraged, starting on day prior to examination	Encouraged, starting on day prior to examination
IV Hydration	N/A	Inpatients: Normal (0.9%) saline infused at 1 mL/kg for 24 hours starting 12 hours prior to contrast exposure (Half-normal saline (0.45%) if patient has evidence of CHF) Outpatients: IV Bolus hydration (250 cc before and after study)	N/A
N-Acetylcysteine (Mucomyst)† (Optional)	N/A	600mg PO BID starting on day prior and for 48 hours after study	N/A
Nephrotoxic Medications	N/A	Discontinue nephrotoxic medications at least 48 hours prior; resume 48 hours after if no evidence of CIN	N/A
Follow-up	N/A	Obtain follow-up serum creatinine in 24 - 48 hours	N/A
* If contrast administration is required in high-risk patients, direct discussion with a radiologist and clinical nephrology service is recommended for a patient-specific imaging and prophylaxis strategy. †N-acetyl cysteine is an optional prophylactic measure for CIN as no convincing evidence of efficacy is available.