BACKGROUND SUBTRACTION - A NEW APPROACH TO THE ASSESSMENT OF DISEASE-ACTIVITY IN CROHNS-DISEASE USING TC-99M-HMPAO-LABELED LEUKOCYTES

A computer-based technique for the quantification of abnormal bowel up take in Crohn's disease has been developed and compared with pre-exist ing clinical, laboratory and scintigraphic methods of assessment. The standard technique for labelling leucocytes with Tc-99m-HMPAO is appli ed. Images were obtained at 40, 120 and 240 min after the injection of radiolabelled leucocytes. The count in the bowel area after subtracti ng background activity corrected to the injected dose and image acquis ition times is the 'scan score', an objective measure of disease activ ity. The scan score is significantly higher in patients with clinicall y active disease (mean 82.1 +/- SEM 13.6) than in those with quiescent disease (24.7 +/- 7.0) (p less than or equal to 0.005). Optimum separ ation between active and quiescent disease is achieved with a threshol d scan score of 20. The scan score was comparable in small bowel disea se (73.3 +/- 16.2), large bowel (94.4 +/- 33) and disease at both loca tions (94.1 +/- 19.2). The scan score correlated favourably with Crohn 's Disease Activity Index (rs = 52, p less than or equal to 0.0001), H arvey and Bradshow Simple Index (rs = 0.4, p less than or equal to 0.0 01), serum C-reactive protein (rs = 0.72, p less than or equal to 0.00 1), serum alpha acid glycoprotein (rs 0.67, p less than or equal to 0. 001), haemoglobin (rs = 0.66, p less than or equal to 0.001), platelet count (rs = 0.47, p less than or equal to 0.006), albumin (rs = 0.61, p less than or equal to 0.0001) and faecal (111)Indium excretion (rs = 0.78, p c 0.001), but not with the ESR (rs = 0.22, p less than or eq ual to 0.4). In 18 patients the scan score was measured serially befor e and after treatment with elemental diet. A reduction in the scan sco re by 70% or more is obtained in 82% of patients who achieved clinical remission, but in only one of eight patients who failed to respond to treatment. The scan score provides an objective measure of disease ac tivity in Crohn's disease and correlates with existing clinical and la boratory activity indices, Excellent correlation was also found with f aecal (111)lndium excretion. The scan score can be used to monitor tre atment and may help define remission.