VALUE OF POSITIVE TC-99M LEUKOCYTE SCANS IN PREDICTING INTESTINAL INFLAMMATION

The value of positive scans of autologous Tc-99m-labelled leucocytes in the detection of intestinal inflammation was assessed in 29 patients with known inflammatory bowel disease and a high probability of intestinal inflammation and 58 with a low probability of intestinal inflammation comprising 37 with intestinal symptoms and 21 with suspected abscess. Autologous leucocytes were labelled with Tc-99m using either of the established methods. In patients with inflammatory bowel disease, 3/13 with ileocaecal and 1/11 with colonic accumulation of Tc-99m were incorrectly diagnosed in that there was no histological evidence of inflammation in those regions. In the low probability patients, all 26 positive images were false positives: there were 19 in the ileocaecal and 7 in colonic regions and no differences between the two subgroups. False positives were more common in low probability than high probability patients (p = 0.011). The results were independent of the Tc-99m cell labelling technique used. Three false positive patients also had normal scans for In-111-labelled granulocytes. The time of first detection of Tc-99m in the bowel was earlier in true than in false positive patients (92% v 33% within 1 h, p = 0.008), the false positive rates in the first hour of imaging being 5% in high and 15% in low probability patients. In Tc-99m scintigraphy, the appearance of the isotope in the intestine occurs commonly in the absence of inflammation irrespective of the cell labelling technique used. In high probability patients, imaging at 1 h can more reliably discriminate true from false positives and retain clinical usefulness. In low probability patients specificity remains unacceptable and Tc-99m-labelled leucocyte scanning in these patients is of little value as a positive predictor of intestinal inflammation.