In the last few decades, as advanced imaging has become pervasive, a few adverse effects relating to its use have been accepted: There are small age-dependent harms suspected from radiation exposure, the underappreciated harms of overdiagnosis and false-positive results, and the deleterious effect on renal function from contrast-induced nephropathy (CIN). It is not unusual for radiology departments to have a renal function cutoff for the use of intravenous contrast or even a protocol requiring hydration or other preventive therapy for those “at risk.”
However, physicians have been wringing their hands over CIN unnecessarily. It may not even be a relevant clinical entity in the context of the emergency department. While many observational studies have documented the substantial incidence of acute kidney injury (AKI) following intravenous (IV) contrast exposure, per the common general definition of CIN, it has been challenging to find a proper control group. Are patients developing subsequent AKI because of the IV contrast or due to the morbidity of the acute illness indicating the need for the CT?
This viewpoint is not new but has been gaining steam over the last few years, particularly in the radiology literature. In 2013, a group from the Mayo Clinic performed a systematic review and meta-analysis of the evidence published prior to 2011 regarding the association with IV contrast exposure and subsequent AKI.1 These authors identified 13 nonrandomized studies comprising 25,950 patients, most of which were published after 2008. There was no statistically significant difference in incidence of AKI, need for dialysis, or death in their comparison, and any trend, if present, actually favored the IV contrast cohort.
Subsequently, these same authors and a group from the University of Michigan published several competing retrospective cohort studies showing differing conclusions.2,3 Each group, with slightly different methodology, presented retrospective single-center analyses of tens of thousands of patients. Again, these were not randomized trials with proper control groups, but rather they used statistical propensity-matching techniques attempting to minimize confounding effects. In the data presented by the University of Michigan, a small increase in the likelihood of AKI was observed in relation to contrast exposure, and the likelihood increased as the glomerular filtration rate decreased. In the data presented by the Mayo Clinic, no association of AKI with contrast exposure was observed.
Finally, most recently, a group from Johns Hopkins University weighed in; call it a tiebreaker. It performed its own slightly different propensity-matching analysis.4 The authors included not only emergency department patients undergoing CT with and without IV contrast but also ED patients not undergoing any advanced imaging. These authors controlled for factors such as critical illness, vital signs, potentially nephrotoxic medication exposures, and comorbid baseline features. In their analysis, again, no association was found between IV contrast exposure and AKI across all their comparison groups.