Study Finds Non-Contrast CT 30 Percent Less Accurate than CECT for Abdominal Pain in the ER

While judicious use of iodinated contrast media (ICM) may remain a point of emphasis in the wake of last year’s global ICM shortage, the authors of a new study caution about the shortcomings of non-contrast computed tomography (CT) for diagnosing abdominal pain in emergency departments (EDs).

For the multicenter study, recently published in JAMA Surgery, researchers examined the use of non-contrast CT in 201 consecutive adult patients (mean age of 50.1) who presented to emergency departments with acute abdominal pain. Out of the 211 patients, 98 patients had a total of 104 primary diagnoses 17 patients had secondary diagnoses and 92 patients had no primary or secondary diagnoses, according to the study.

After the establishment of a reference standard with dual-energy contrast-enhanced CT (CECT) in these patients, researchers digitally subtracted oral and IV contrast media. Then the study authors assessed the performance of three specialist faculty radiologists and three radiology residents who interpreted the unenhanced CT scans.

Specialist radiologist faculty and radiology residents had a 70 percent accuracy rate overall for interpreting unenhanced CT, according to the study authors.

“It is important to understand the risk of withholding contrast medium so informed risk-benefit analyses can be made. In this consecutive cohort of ED patients presenting with abdominal pain, unenhanced CT was consistently approximately 30 percentage points less accurate than contrast-enhanced CT for primary and secondary actionable findings,” wrote Matthew S. Davenport, M.D., who is a William Martel Collegiate Professor of Radiology and co-director of the Ronald Weiser Center for Prostate Cancer within the Division of Abdominal Radiology at the University of Michigan, and colleagues.

(Editor’s note: For related content, see “Study Looks at Capability of AI for Detecting Overlooked Liver Metastases on CECT,” “Could Photon Counting CT Supplant MRI for Imaging Assessment of Hepatic Steatosis?” and “Seven Takeaways from Best Practice Recommendations for Incidental Radiology Findings in the ER.”)

For primary diagnoses, the study authors said the faculty radiologists had higher accuracy rates than the residents (82 percent vs. 76 percent). While reviewing residents had better accuracy rates for actionable secondary diagnoses (90 percent vs. 87 percent for faculty radiologists), Davenport and colleagues said false-positive and false-negative diagnoses had an impact with these statistics. For faculty radiologists, there were fewer false-negative results for patients with primary diagnoses (38 percent vs. 62 percent for residents) and a greater percentage of false-positive secondary diagnoses (63 percent vs. 37 percent for residents).

The study authors pointed out that faculty radiologists had false-positive rates with unenhanced CT that ranged between 10 to 21 percent and false-negative rates ranging between 13 to 19 percent. Reviewing radiology residents had false-positive rates ranging between 8 to 19 percent and false-negative rates between 15 to 27 percent.

“False-negative results at unenhanced CT may occur due to misdiagnosis or underdiagnosis and false-positive results may occur from impaired radiologist confidence. These errors can harm patients, delay care, and result in additional unneeded testing and intervention,” maintained Davenport and colleagues.

Beyond the inherent limitations of a retrospective study, the authors acknowledged that the unenhanced CT data was generated by subtracting oral and IV contrast medium from the study’s reference standard. They also conceded that the use of single-energy, non-contrast CT may have resulted in different diagnostic accuracy rates.