Sampling intervals in dynamic scintigraphy in lower gastrointestinal haemorrhage

The sampling rate for 99mTc RBC scintigraphy in acute LGIH is quite variable. More rapid sampling allows more accurate localisation spatially by detecting bleeding more accurately temporally which minimises the impact of rapid peristalsis on localisation errors. There has been no specific investigation reported in the literature comparing the diagnostic efficiency of various sampling intervals.Methods: This research was a retrospective clinical study of 49 99mTc red blood cell studies. Each was interpreted by four independent physicians as both five minute dynamic data and one minute dynamic data. The relative contribution of each sampling interval to bleed detection, bleed localisation and interpretive confidence was recorded.Results: Generally, approximately 90% of the relative contribution to bleed detection and interpretive confidence was attributed to one minute sampling. Five minute sampling was seen to have the greatest impact on bleed localisation (28%). One minute sampling extends an advantage to minimising false positives while five minute sampling plays a role in reducing false negatives.Conclusion: False positive studies can be reduced by predominantly relying on the one minute dynamic data for bleed detection. One minute dynamic data should be reframed to five minute intervals to assist in bleed localisation. This need only be undertaken when a bleed has been identified on the one minute dynamic data.