How common is contrast nephropathy in the general outpatient setting? When you send one of your outpatients to get a CT scan with iv contrast, what is the real risk? Much of the randomized, controlled trial data on contrast nephropathy comes from INPATIENTS undergoing angiography or other procedures, often focusing on those with the greatest perceived risk of contrast nephropathy (e.g., diabetics, those with underlying CKD to begin with) in order to generate enough meaningful datapoints for analysis. An article by Mitchell et al in this month’s CJASN reports the risk of contrast nephropathy in a mixed OUTPATIENT group–and finds that the risk of contrast nephropathy may actually be higher than what has generally been appreciated.
One big caveat, in my mind: even though the article is entitled, “Incidence of contrast-induced nephropathy after contrast-enhanced computed tomography in the outpatient setting,” the phrase “outpatient setting” should be examined a little more closely. Their patient population wasn’t exactly “outpatient” as we normally think of it; it was all the patients entering a large, academic emergency department who underwent CT scans with iv contrast. One could argue that by the very nature of their showing up in an emergency department (as opposed to their primary care physician office) they could be seen as “sicker” and therefore more susceptible to the effects of iv contrast use. Nonetheless, the researchers found that the incidence of contrast nephropathy (defined as an increase in serum creatinine greater than 0.5 mg/dL or greater than 25% of baseline between 2-7 days after contrast administration) was 11% (70 out of 633 patients receiving iv contrast), which is quite high. Not surprisingly, the development of CIN was also associated with an increased risk for developing severe renal failure and death.
There’s still a lot of controversy about contrast nephropathy and just how significant it is–after all, the vast majority of patients see a return of their creatinine to baseline levels–but perhaps the knowledge that over 10% of patients in an emergency department show evidence of renal injury with a simple CT scan with iv contrast should make us think twice about ordering this test so frequently.