Background

Intravenous (IV) iodinated contrast media is used routinely to improve the accuracy of computed tomography (CT) in the emergency department (ED).  Prior studies have linked contrast media with the development of acute kidney injury (AKI) and has been linked to increased risk of major adverse events including the initiation of dialysis, renal failure, stroke, myocardial infarction and death.   To date, we have understood contrast-induced nephropathy (CIN) based on studies that predate the common use of low- and iso-osmolar contrast media.  Additionally, most of our literature on the subject is based on findings from arterial angiographic studies rather than more typical intravenous contrast studies performed in the ED.

Clinical Question

Does the use of IV contrast for CT scans in the ED increase the incidence of AKI?

Population

Patients aged 18 years and older who received a CT with or without IV contrast in the ED during the study period were included in the study. Patients must have had both an initial serum creatinine level measured in the 8 hours before CT as well as a second level measured 48-72 hours after the CT was performed.

Intervention

IV contrast enhanced CT scan

Control

Non-IV contrast enhanced CT scan and no CT scan

Outcomes

Primary: Incidence of AKI defined as an absolute increase in serum creatinine by > 0.5 mg/dl or > 25% increase from baseline serum creatinine at 48-72 hours or by the AKI Network/Kidney Disease Improving Global Outcomes Guidelines
Secondary: New chronic kidney disease, dialysis, and renal transplantation at 6 months

Design

Retrospective, single center study

Excluded

Patients were excluded if their initial serum creatinine level was less than 0.4 mg/dL (this was done to minimize the inclusion of random laboratory error as cases of AKI). Additionally, patients who had an initial serum creatinine level greater than or equal to 4.0 mg/dL were excluded as they already met partial criteria for severe AKI. Other exclusion criteria included insufficient serum creatinine level data, a history of renal transplant, ongoing or previous dialysis, an ED visit in the 6 months before the study start date, a CT scan performed in the 6 months preceding the index ED visit, and a contrast CT performed within 72 hours of ED departure. The authors chose to exclude the preceding 6-month period and the following 72-hour period to minimized potential confounding effects of other administered IV contrast.

Primary Results

Primary Results

  • 17, 934 patient visits from 16, 801 unique patients were included.
  • Patients included those who underwent contrast-enhanced CT, underwent unenhanced CT without contrast, and patients who received no CT at all.
    • 7, 201 patients underwent contrast-enhanced CT
    • 5, 499 patients underwent unenhanced non-contrast CT
    • 5, 234 patients had no CT imaging

Critical Results

  • Multivariate logistic regression modeling was performed and found no independent effect of contrast media on the probability of developing AKI
    • CIN criteria: OR = 0.96 (95% CI: 0.85 – 1.08)
    • Acute Kidney Injury Network/Kidney Disease Improving Global Outcomes criteria: OR = 1.00 (95% CI 0.87-1.16)
  • Factors found to be strongly associated with an increased probability of AKI
    • Increased age
    • Nephrotoxic medications
    • Preexisting diagnosis of congestive heart failure, chronic kidney disease or hypoalbuminemia.
  • The administration of IV crystalloids was associated with a lower probability of AKI

Strengths

  • Large sample size powered to detect a difference in AKI incidence of 1.5%
  • Study of IV rather than intra-arterial contrast making the results more relevant to the ED
  • Used multiple definitions of AKI to ensure incidence wasn’t under-reported
  • Propensity-score matching was used to overcome issues of selection bias

Limitations

  • Single academic medical center ED
  • The majority of patients were admitted to the hospital and thus may be more ill than patients being discharged, ultimately overestimating the incidence of AKI in the population
  • There may have been a selection bias by clinicians for which patients were given contrast and which were not
  • Different treatments were given to patients based on their baseline renal function and whether they were going to get IV contrast or not. This may have affected the results in favor of no association with AKI
  • The retrospective analysis required data from the electronic medical record, so undocumented comorbidities or outcomes would have been missed
  • If a patient sought treatment for an adverse outcome at an outside hospital it would have been missed

Author's Conclusions

"In the largest well-controlled study of acute kidney injury following contrast administration in the ED to date, intravenous contrast was not associated with an increased frequency of acute kidney injury.”

Our Conclusions

We agree with the authors conclusions. Although the methodology wasn’t the preferred one for finding causality, there does not appear to be any association between administration of IV contrast for a CT scan with the current contrast agents used and the development of AKI in this group of patients.

Potential Impact To Current Practice

When faced with the decision to administer IV contrast for a CT scan, we should consider giving contrast if needed for diagnostic accuracy without the previously held concern for CIN.

Bottom Line

Current low-osmolar and iso-osmolar contrast agents appear safe to be used when needed in patients without leading to a significant occurrence of CIN. This data justifies the performance of a prospective randomized trial to further investigate the issue.

Read More

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