Contrast Induced Nephropathy: A Modern-Day Medical Myth

Background: Computed tomography (CT) scans using IV contrast agents are one of the most common imaging modalities used in the emergency department (ED). The reason for this is no secret. CT scans with IV contrast offer a large amount of information on patients when limited information is available, they are diagnostic of many conditions with good performance characteristics, and they are often requested by consultants.   Many patients get suboptimal studies without IV contrast due to fear of contrast induced nephropathy (CIN). However, more recent studies suggest that with the use of iso- and low-osmolar contrast agents (almost universally used today) this concern is unwarranted.  Most studies on this topic have focused on unselected populations, and not focused on patient groups at higher risk for AKI, including those with sepsis.

What They Did:

• Single-center retrospective propensity matched cohort analysis
• Determine the risk for acute kidney injury (AKI) attributable to IV contrast media (CM) in patients with sepsis

Outcomes:

• Primary: Incidence of AKI
  • SCr increased by at least 0.3mg/dL OR
  • 5x increase over baseline SCr at 48 – 72hrs

Inclusion:

• Age ≥18 years
• Sepsis diagnostic criteria
• Serum creatinine (SCr) measured on arrival in ED and again at 48 – 72hrs later

Exclusion:

• Prior ED visit within 7d (to limit confounding of pre-exisiting hospital-acquired AKI)
• Initial SCr <0.4mg/dL (to minimize inclusion of random laboratory error as cases of AKI) or >4.0mg/dL (already meeting partial criteria for severe AKI)
• Insufficient SCr data
• On Hemodialysis
• Prior CT scan performed within 72hrs

Results:

• 4171 ED Visits
  • 1464 Contrast Enhanced CT (CECT)
  • 976 Unenhanced CT
  • 1731 No CT
• Incidence of AKI:
  • CECT: 7.2%
  • Unenhanced CT: 9.4%
  • No CT: 9.7%
  • Contrast media was not associated with AKI in septic patients (OR = 0.93; 95% CI 0.71 – 1.20)
  • Factor most associated with development of AKI were pre-existing diagnosis of CHF (OR 2.50; 95% CI 1.89 – 3.30)

Strengths:

• Large sample size
• First study to evaluate the relationship between IV contrast and AKI in septic patients
• To minimize selection bias, associated with imaging, the authors included a second control group of patients who met the same inclusion criteria but did not undergo CT imaging
• Propensity score matching used to minimize selection bias due to covariate variables (However this cannot include all factors that could impact decisions to administer CM)

Limitations:

• Retrospective study design limits analysis to events recorded in EHR
• Primary outcome is a lab-oriented outcome and not a patient-oriented outcome
• Single center study
• Although propensity score matching was done, it is unclear why contrast or non-contrast studies were obtained in the particular groups
• Most patients admitted to hospitals for >2 days, however some were discharged before the 48hr mark, and therefore some cases of AKI may have been missed
• Some baseline characteristics were not well balanced between groups
  • Serum creatinine was lower in the CECT group (0.9mg/dL) vs unenhanced CT group (1.2mg/dL)
  • More patients with diabetes mellitus in unenhanced CT (31%) vs CECT (22%)
  • More CHF patients in unenhanced CT (25%) vs CECT (15%)
• ≈35% of patients did not get a baseline SCr value during the appropriate timeframe
• Baseline SCr values were lower in the contrast enhanced CT group (0.9mg/dL) compared to the unenhanced CT and non-CT groups (1.2 and 1.0mg/dL respectively) which could bias results in favor of contrast enhanced CT group

Discussion:         

• Older studies that demonstrated an association between contrast and AKI were performed when contrast media was hyperosmolar and given in larger volumes than what are used today
• Many of the older trials were also performed without control groups that did not receive contrast
• Many current studies suffer from selection bias, where providers withhold contrast in clinical scenarios where the risk for AKI is perceived to be high (SCr >4.0mg/dL, renal transplant, etc…)

Author Conclusion: “Sepsis is a medical emergency proven to benefit from early diagnosis and rapid initiation of treatment, which is often aided by CECT. Our findings argue against withholding CM for fear of precipitating AKI in potentially septic patients.”

Clinical Take Home Point: Despite this being a single center, retrospective analysis of septic patients, this is another study, showing an absence of association between contrast media and AKI.

If you have a septic patient, with a SCr <4.0 mg/dL and without a renal transplant, requiring contrast for diagnosis…Give the contrast!!!.

References:

1. Hinson JS et al. Acute Kidney Injury Following contrast Media Administration in the Septic Patient: A Retrospective Propensity-Matched Analysis. J Crit Care 2019. PMID: 30798098

For More Thoughts on This Topic Checkout:

• REBEL EM: Is Contrast Induced Nephropathy (CIN) Really Not a Thing?
• REBEL EM: Contrast Induced Nephropathy (CIN): Fact or Myth?
• REBEL EM: The AMACING Trial: Prehydration to Prevent Contrast Induced Nephropathy (CIN)?

Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)