Comparison of technetium 99m nanocolloid and indium 111 leucocytes in the diagnosis of orthopaedic infections.

It has been suggested that technetium 99m nanocolloid is as effective an inflammatory radiopharmaceutical as indium 111 leucocytes. This study compares the efficacy of 99Tcm nanocolloid and 111In leucocytes in the detection of orthopaedic infection in 19 patients with a high clinical suspicion of infection. The two scintigrams were performed within 24 h of each other. A scintigram was considered positive where there was an increase in tracer uptake at the site of interest. Concordance rate of 73% was achieved. The numbers of false positives with 111In leucocytes and 99Tcm nanocolloid were three and six respectively. The single false negative in both was of a patient with tuberculous spondylodiscitis. Sensitivity was 75% in both. Specificities were 79% and 60% for 111In leucocytes and 99Tcm nanocolloid respectively. Positive Predictive Value was only 33% with 99Tcm nanocolloid and 50% with 111In leucocytes. 99Tcm nanocolloid also proved less reliable in accurately detecting infected prostheses. We conclude that 99Tcm nanocolloid cannot replace 111In leucocytes in the diagnosis of orthopaedic infections.