Written by Alex Chen, MD.
In this meta-analysis, contrast-enhanced CT scan vs non-contrast CT did not show significant differences in rates of acute kidney injury (AKI), need for renal replacement therapy (RRT), or mortality.
Why does this matter?
Every clinician has to think about the risk of contrast-induced nephropathy in their patients. Whether this occurs once in a blue moon or a dozen times a day, this can create unnecessary admissions for IV fluid prior to repeat scans with contrast or deference to sub-optimal imaging. Previous studies have shown that patients with post-contrast AKI had longer hospital stays and higher mortality compared to those who did not have AKI. But there is a growing body of literature that shows that the incidence of contrast-induced nephropathy may not be as high as previously reported.
This meta-analysis looked at 107,335 patients in a variety of settings (ED, ICU, other). All studies were observational, with a majority being retrospective in nature. The primary outcome was development of AKI, as defined by the individual study. Secondary outcomes included need for RRT and all-cause mortality. It is important to note that they excluded articles on pediatrics and intra-arterial procedures, the latter being a group of patients which have had higher reports of post-contrast AKI. The authors found contrast-enhanced CT was not significantly associated with AKI (OR 0.94; 95% CI 0.83-1.07), need for renal replacement therapy (OR 0.83; 95% CI 0.59-1.16), or mortality (OR 1.0; 95% CI 0.73-1.36). The osmolality of the contrast also did not seem to make a difference in their subgroup analysis. There was only one study included with high-osmolality contrast (Heller et al., Med J Aust 1991), which did not show a significantly increased risk of AKI with high-osmolality contrast vs non-contrasted CT.
That sums up the findings of this meta-analysis, but read on to learn more.
The rest of the story
The ACR Manual on Contrast Media from May 2017 makes a differentiation between contrast-induced nephropathy (CIN) and post-contrast acute kidney injury (PC-AKI). The reason for this differentiation is that we don’t know whether the AKI is actually due to contrast administration or if there are concomitant disease processes creating this effect. This is further complicated because these terms are often used interchangeably in the literature along with varying definitions for AKI. Creating a RCT that looks at this question is improbable because of the inherent differences in the indications for contrasted versus non-contrasted studies. For example, it is unethical for a patient with a possible pulmonary embolism to be randomized to contrast versus non-contrasted scan. Physicians are also less likely to utilize a contrasted scan on a patient at higher risk for AKI. Another source of bias may be the need to have a follow-up creatinine measurement at 72 hours, which may select for a sicker group of patients requiring hospitalization. This study builds on the article by Hinson et al. that came out earlier this year that did not find an association between IV contrasted scans and AKI in a retrospective cohort analysis of ED patients. The most recent ACR recommendations have placed a soft threshold of eGFR ≥30, and they acknowledge that this is a source of contention. I think I will still be bound by my institutional rules for now, but I will be pushing more to get the scans with contrast I deem are necessary.
Acute Kidney Injury After Computed Tomography: A Meta-analysis. Ann Emerg Med. 2017 Aug 12. pii: S0196-0644(17)30881-8. doi: 10.1016/j.annemergmed.2017.06.041. [Epub ahead of print]
- This is the large retrospective cohort mentioned. Hinson JS et al. Risk of Acute Kidney Injury After Intravenous Contrast Media Administration. Ann Emerg Med. 2017
- This is 129 pages of contrast lovin' that Alex read to make sure this information was accurate. Dang... ACR Manual on Contrast Media – Version 10.3; 2017. 35-42.