Comparison of Tc-99m Infecton imaging with radiolabelled white-cell imaging in the evaluation of bacterial infection

Background Bacterial infection can pose a substantial diagnostic dilemma. Techniques involving radiolabelled leucocytes can pinpoint the site of inflammation. However, previous radiolabelling techniques have failed to distinguish between bacterial-mediated infection and non-bacterial inflammation. To overcome this difficulty, we have studied a radiopharmaceutical, technetium-99m (Tc-99m) Infecton, which is based on the antibiotic ciprofloxacin. Methods We used this agent to image bacterial infection in 56 patients (one twice) with known or suspected sites of infection. We then compared the imaging results of these patients with those from a radiolabelled leucocyte study. Findings The concordance rate was 68% (39 out of 57 images). In 18 discordant results Tc-99m Infecton was correctly positive in 8 out of 9 positive studies and correctly negative in 4 out of 9 negative studies. 4 out of 5 of the falsely negative studies were in patients who had taken antibiotics for over 7 days. We found that Tc-99m Infecton gave better imaging results than radiolabelled leucocytes. Comparison between Tc-99m infecton and leucocyte imaging gave sensitivities of 84% and 81%, and specificities of 96% and 77%, respectively. Interpretation We believe that the specificity Tc-99m Infecton confers for bacterial infection and its ease of administration are the main advantages of this new agent.