Does IV contrast really cause kidney injury?
The concept of Contrast-Induced Nephropathy (CIN) has long been accepted as a real, clinically relevant entity. However, this is now being questioned after a recent article was published in the Annals of Emergency Medicine…
You should really read this study, but in summary, it is a single center, retrospective analysis over 5 years comparing patients who got CT scans with and without contrast, looking to see if acute kidney injury (AKI) could be attributable to contrast use.
The takeaway point, of course, is that intravenous contrast was not associated with an increased frequency of acute kidney injury.
This finding has been met with excitement…
You may be thinking at this point that a lone retrospective study done at a single institution should not be enough to change such a long held practice, and you may be right. The authors of the study themselves state that a well-done, randomized control trial is still necessary.
But this is not the first study that should have us questioning the existence of CIN. Especially given the data on which we currently hold our beliefs is not so strong.
In April 2013, McDonald et al published a systematic review and meta-analysis of controlled studies on the topic, and found similar rates of important clinical outcomes (AKI, dialysis, death) in the contrast and no-contrast cohorts.
The Davenport study showed there was an increase in AKI in the contrast group, but only in the subset of patients with a starting GFR < 30 mL/min per 1.73 m2.
The McDonald study showed increased risk of AKI with lower GFR, but this was true in both groups, suggesting that pre-existing kidney disease is a risk factor for AKI, regardless of IV contrast use or not.
So where did this idea of CIN come from? One suggestion is that patients who get CT scans are often ill, and perhaps it is the illness itself and not the IV contrast that is causing the AKI. The studies on which we base our understanding of CIN may not have properly controlled for the underlying disease process which led to the CT scan. Recent studies may have done a better job of this.
Ok, so where does this leave us?
To which patients can we safely give IV contrast? Does CIN even exist at all?
Let’s ask the radiologists!
According to the American College of Radiology Manual on Contrast Media…
So there may come a day when we do not use any threshold at all. But for now, you should be comfortable giving IV contrast to patients with a GFR > 30.
If this is not the practice at your institution, it is time to have a productive discussion with your radiology department and get in line with the ACR guidelines.
A final point:
In the end, it comes down to risk vs. benefit.
At this time, we do not yet know the true significance of CIN, but it seems obvious we are overestimating the risk of harm from IV contrast.
If you feel the benefit of diagnosing a life-threatening condition outweighs the theoretical risk of CIN, go ahead and give that contrast.
UPDATE (12/11/17): Another study, a meta-analysis in the Annals of EM, again showed no difference in acute kidney injury between patients receiving contrast-enhanced and non-contrast CT.
See a review of that article here:
Aycock, Ryan D., et al. “Acute Kidney Injury After Computed Tomography: A Meta-analysis.” Annals of Emergency Medicine (2017)