Scintigraphic determination of equivocal appendicitis

We evaluated Tc-99m-labeled anti-CD15 immunoglobulin M monoclonal antibody (LeuTech) for scintigraphic detection of acute appendicitis in patients with an equivocal clinical presentation. LeuTech avidly binds to circulating and sequestered human polymorphonuclear neutrophils in vivo eliminating the need for in vitro cell labeling and the risks of blood handling. We studied 99 patients to evaluate the safety and efficacy of LeuTech imaging. Serial dynamic and static planar images were acquired for up to 3 hours after the intravenous administration of 10 to 20 mCi of Tc-99m LeuTech. Scans were read as positive or negative for acute appendicitis or other intra-abdominal infection. The institutional diagnosis was established by surgery and histopathology of the appendix, results of other diagnostic studies, or 2-week clinical follow-up. Scans were positive for appendicitis in 39 of 40 patients with appendicitis at surgery (sensitivity 98%) and negative for appendicitis in 49 of 58 patients without appendicitis (specificity 84%). One was lost to follow-up. Accuracy, positive predictive value, and negative predictive value were 90, 81, and 98 per cent respectively. In patients with appendicitis and positive scans more than 50 per cent of the images were positive at 4 minutes, and all were positive by 1 hour. Mean time of first positive image was 15 minutes. There were no serious adverse reactions. We conclude that LeuTech imaging is a highly sensitive test for detection of appendicitis in equivocal cases. There are advantages of this agent over the other currently used radiotracers in terms of convenience and time to diagnosis particularly the rapidity with which acute appendicitis will be seen on the images.