Radiolabelled granulocytes in inflammatory bowel disease

Radiolabelled granulocytes in chronic inflammatory bowel diseases (CIBD) are able to diagnose the disease extent and assess the disease activity. It may be performed with 111In oxine- and 99Tcm hexamethylpropyleneamineoxime (HMPAO)-labelled cells. The granulocyte scan localizes inflamed bowel segments with an accuracy comparable with radiology and endoscopy including biopsy of the bowel (r = 0.95; P < 0.001). The specificity of the scan for diseased segments is near 100%, the sensitivity 92%. A three-phase white blood cell scan (imaging: 0.5, 4, 20 h post injection) allows differentiation of diseased bowel segments from abscesses and fistulas. False positive results are possible in necrotic carcinomas. The 99Tcm HMPAO scan shows rapid renal and delayed biliary and intestinal excretion of tracer. In this way diagnostic problems arise in the small pelvis. Because of the intestinal and biliary excretion, early images should be obtained (0.5–2 h post injection). Later scans with 99Tcm HMPAO are of minor importance. The disease activity can very specifically be assessed by the determination of the percentage faecal 111In excretion (96 h faecal collection). Active and non-active diseases can be clearly differentiated. We found no correlation with the subjectively influenced Crohn's disease activity index (CDAI) (r = 0.25; P < 0.05), but good correlations with the Dutch Index (van Hees: r = 0.67), ESR (r = 0.69), serum albumin (r = −0.54) and orosomucoid (r = 0.65). The percentage faecal excretion correlates well with the histologically estimated leucocytic bowel infiltration. Because of the intestinal 99Tcm HMPAO excretion the determination of faecal excretion is pointless in 99Tcm studies. In these studies a semiquantitative scan grading (comparison of bowel activity with bone marrow, liver and spleen activity) correlates acceptably with the percentage faecal excretion. A scan activity index (number of diseased segments × scan grading) is superior. The granulocyte scan is indicated in primary diagnosis of CIBD especially in very acute disease and in bowel stenoses where there is danger of bowel perforation during colonoscopy and in suspected abscesses or fistulas.