CT with a low radiation dose appears to be as good as standard-dose CT for diagnosing teens and young adults with suspected appendicitis, a randomized trial showed.
The rate of appendectomies performed in which the organ was not actually inflamed was 3.5% using low-dose CT and 3.2% with standard-dose CT, according to Kyoung Ho Lee, MD, of Seoul National University in South Korea, and colleagues.
The difference between the two groups came in below the 5.5 percentage point threshold for noninferiority, consistent with prior exploratory studies of low-dose CT for diagnosing appendicitis, the researchers reported in the April 26 issue of the New England Journal of Medicine.
"These results can be attributed to the excellent imaging capability of modern CT scanners and the intrinsic simplicity of CT-image interpretation in diagnosing appendicitis, which may offset the loss in image quality due to low-dose CT techniques," they wrote.
CT has become the main tool for diagnosing acute appendicitis in adults, but exposure to radiation -- and the possible effects on cancer risk -- are of concern in children and young adults.
Lower-dose protocols have not been widely accepted because of concerns about inadequate image quality that had not been resolved in randomized studies.
So Lee and colleagues conducted a randomized, noninferiority trial at their center. It included 879 patients ages 15 to 44 with suspected appendicitis.
Roughly half received a low-dose CT scan (median radiation dose 116 mGy/cm) and half received a standard-dose scan (median radiation dose 521 mGy/cm).
About 40% of patients in each group had an appendectomy after the scan. It was later determined that six patients in each group (3.5% in the low-dose group and 3.2% in the standard-dose group) had organs free of inflammation, and thus underwent an unnecessary operation.
Based on the absolute difference in the negative appendectomy rate between the two groups, the researchers determined that using low-dose CT instead of standard-dose in 330 patients would result in one additional unnecessary operation, a risk, they noted, that can be weighed against the potentially higher cancer risk with the standard dose.
"However, it is highly debatable whether the radiation levels used in our two groups can actually induce cancer and whether use of the low dose instead of the standard dose can actually reduce the carcinogenic risk," they added.
The rate of perforated appendix -- an indicator of delayed diagnosis -- was similar in the low-dose and standard-dose groups (26.5% versus 23.3%, P=0.46).
Although diagnostic performance was similar in the two groups, the confidence clinicians had in the diagnosis tended to be higher when standard doses of radiation were used.
The percentage of patients who needed additional imaging tests was nonsignificantly higher in the low-dose group (3.2% versus 1.6%, P=0.09), and there was a significantly longer interval between the initial scan and the operation for patients in the low-dose group (7.1 hours versus 5.6 hours, P=0.02).
Both of those findings "may represent the referring physicians' hesitation to base their decisions on the low-dose CT findings," Lee and colleagues wrote.
Nevertheless, they wrote, "our results indicate that low-dose CT, despite its limitations, may be used instead of standard-dose CT as the first-line imaging test, because the ultimate clinical outcomes and diagnostic performance can be maintained if low-dose CT is incorporated into the diagnostic process with selective additional imaging and clinical observation."
They acknowledged that the study could have been biased toward low-dose CT because investigators with experience in low-dose CT had a major role in caring for the patients.
The study was supported by a grant from GE Healthcare Medical Diagnostics in Korea, a Mid-Career Researcher Program grant from the National Research Foundation of Korea, and a grant from the Seoul National University Bundang Hospital Research Fund.
The authors reported that they had no conflicts of interest.
- Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner
New England Journal of MedicineSource Reference: Kim K, et al "Low-dose abdominal CT for evaluating suspected appendicitis" N Engl J Med 2012; 366: 1596-1605.