# Rethinking Contrast CT in the Emergency Department: Why Pretest Probability, Not Creatinine, Should Guide Our Decisions

## TL;DR

This paper argues that emergency department decisions about contrast CT should prioritize pretest probability over creatinine levels to improve diagnostic accuracy and patient outcomes.

## Contribution

The paper highlights the shift from creatinine-based to clinically driven CT decision-making in emergency care.

## Key findings

- Contrast-associated acute kidney injury is rare in the general ED population.
- Noncontrast CT is less accurate for diagnosing high-risk emergency conditions.
- Diagnostic decisions should focus on clinical necessity rather than avoiding contrast.

## Abstract

Contrast-enhanced CT plays a central role in diagnostic decision-making in the emergency department (ED). However, contrast administration is often delayed or avoided mainly based on serum creatinine levels, despite increasing evidence that the nephrotoxic risk of modern iodinated contrast agents is low. Such creatinine-centered decision-making may result in diagnostically inadequate imaging and delayed diagnosis of time-sensitive, high-risk conditions in emergency care.

This commentary examines the persistence of creatinine-centered imaging heuristics and their diagnostic consequences in emergency care, while not proposing new guidelines. Contemporary evidence shows that contrast-associated acute kidney injury (CA-AKI) is uncommon in the general ED population, with modest risk increases limited to patients with severe chronic kidney disease. In comparison, noncontrast CT is substantially less accurate for many high-risk emergency conditions, including vascular, ischemic, and infectious pathologies. Basing imaging decisions on the avoidance of contrast rather than diagnostic necessity can encourage defensive practice and undermine clinical reasoning.

CT selection in the ED should be guided primarily by pretest probability and diagnostic intent, with renal function serving as a contextual consideration rather than a gatekeeper. Refocusing imaging decisions on clinical purpose aligns practice with current evidence and supports timely, accurate diagnosis. Cultivating this reasoning skill should be recognized as a core competency in emergency medicine.