Neutrophil-specific Tc-99m-labeled anti-CD15 monoclonal antibody imaging for diagnosis of equivocal appendicitis

We evaluated Tc-99m-labeled anti-CD15 immunoglobulin M monoclonal antibody (LeuTech) for diagnosing acute appendicitis in patients with an equivocal c linical presentation. LeuTech avidly binds to circulating and sequestered h uman polymorphonuclear neutrophils in vivo, eliminating in vitro cell label ing and blood handling. Methods: We studied 49 patients to evaluate the saf ety and efficacy of LeuTech imaging. Tc-99m-labeled LeuTech was prepared on site using a lyophilized kit, Tc-99m-labeled pertechnetate, and 2 differen t incubation techniques, 1 at room temperature and the other at 37 degrees C. The abdomen was serially imaged for up to 3 h after the intravenous admi nistration of 370-740 MBq Tc-99m-labeled LeuTech. Scans were read as positi ve or negative for acute appendicitis or other intraabdominal infection. Th e institutional diagnosis was established by surgery, other diagnostic stud ies, or 1-mo clinical follow-up. Results: Scans were positive for appendici tis in all 26 patients with appendicitis, for a sensitivity of 100%, and ne gative for appendicitis in 19 of 23 patients without appendicitis, for a sp ecificity of 83%. Accuracy, positive predictive value, and negative predict ive value were 92%, 87%, and 100%, respectively. Results were not different between the LeuTech preparations. The rate of laparotomies with negative f indings in patients who underwent surgery was 10%. The average time from in jection to LeuTech visualization in the appendix for cases positive for app endicitis was 9 min. No serious adverse reactions occurred. Conclusion: Leu Tech imaging is safe, rapid, and sensitive for diagnosis of appendicitis in equivocal cases. The potential advantages of LeuTech over currently availa ble radiopharmaceuticals for infection imaging are ease of preparation, abs ence of blood handling, excellent image quality, no requirement for SPECT, and rapid diagnostic uptake.