Oral contrast unnecessary in many abdominal CT scans

Abdominal CT scans can be performed markedly faster and with no loss of accuracy by using intravenous contrast only, rather than the more conventional IV plus oral contrast, according to two studies presented at the annual meeting of the Society for Academic Emergency Medicine.

Patients with abdominal pain tolerate oral contrast poorly. It takes them a long time to drink it — and all the while, they’re occupying an emergency department (ED) bed and a nurse’s time, with corresponding delays in their diagnosis and treatment. Two groups of investigators wondered if oral contrast could be omitted. The answer appears to be yes, based in their findings.

Presented interim results from an ongoing randomized trial of 193 adult ED patients who underwent abdominal CT because they were deemed to have an indeterminate clinical probability of acute appendicitis. Patients were assigned to IV contrast only or IV plus oral contrast.

A total of 33% of patients were diagnosed with acute appendicitis by the trial’s two blinded radiologists, a diagnosis subsequently confirmed by surgical pathology.

The IV-only contrast imaging had 98.6% diagnostic sensitivity and 99.2% negative predictive value. Oral plus IV contrast had 100% sensitivity and 100% negative predictive value. The two radiologists reached discrepant decisions in 11 cases: 5 in the IV-only contrast group, and 6 in the IV plus oral contrast group, said an emergency physician at York (Pa.) Hospital.

In a separate presentation at the meeting of the University of Utah, Salt Lake City, reported on 114 patients who had abdominal CT with IV-only contrast ordered for suspected acute appendicitis, diverticulitis, bowel obstruction, or free air, and 627 other patients who had CT with IV and oral contrast for the same indications during the 3 months immediately before an ED ‘policy shift favoring IV-only contrast.’

The mean time from test order to completion was 108 minutes in the IV plus oral contrast group, significantly longer than the 46 minutes with IV contrast only. The radiologists’ reading time was 56 minutes for images obtained with IV plus oral contrast, and significantly less at 4 minutes with IV contrast only.

Six patients in the IV-only group were rescanned because radiologists deemed their initial scans insufficient. But only one of the six had a change in diagnosis, to inflammatory bowel disease.

“Oral contrast is not required for focused abdominal CT to evaluate for these four conditions.”

One member expressed surprise that the time from ordering the CT to its completion was only 62 minutes faster with IV-only contrast. “At my place, once the patient finishes drinking, the scan can only be done on the next legal holiday,” that the mean 46-minute time to scan completion in the IV-only group can probably be shortened further.