Evaluation of Tc-99m leukocyte scan in the diagnosis of acute appendicitis.

A new 99mTc Microlite leukocyte scan was performed in 38 patients to assess its value in the diagnosis of acute appendicitis. Autologous leukocytes are labeled with 99mTc by inducing phagocytosis of 99mTc albumin microcolloid particles. The advantages of this test over the standard indium-111 scan include superior imaging capability, a marked reduction (greater than 75%) in the radiation dose, and performance of the test including labeling, in less than 3 hr. Imaging is performed at 5-90 min postinjection of labeled cells. There were 19 male and 19 female patients with ages ranging from 10 to 80 years, in whom the diagnosis of appendicitis was indeterminate on clinical examination. Of the 13 of the 38 patients (34%) who came to surgery 12 had acute appendicitis. The WBC scan correctly identified 10 of the 12 cases of appendicitis. There were two false-negative studies. In the nonoperative group of 25 patients admitted for observation, 21 studies were reported as negative and four identified other sites of inflammation. All patients with a negative study have remained asymptomatic on follow-up. With a sensitivity of 83% (10/12) and a specificity of 100% (26/26) the 99mTc leukocyte scan provides a rapid and highly accurate method for diagnosis of appendicitis in this preliminary study of patients with equivocal clinical exams.