Non-compliance does not impair qualitative evaluation of colonic transit time

Abstract

Measurement of colonic transit time (CTT) by using radiopaque markers with the "Multiple ingestion-Single film" technique is a simple, reproducible technique to measure total and segmental CTT. However, it requires good compliance of the patients, who must ingest the capsules containing radio-opaque markers for 6 consecutive days. The purpose of this study was to estimate the error in CTT measurement if they fail to do this. The protocol tested was to ingest 12 markers per day during 6 days and take a plain film of the abdomen on day 7. The study was done by simulation using a 3-compartiment model (right colon, left colon, rectosigmoid area). There was a set of 67,525 possibilities with possible single or double failure of markers ingestion for 6 days either 238,266 combinations for one omission, or 312,375 combinations for two omissions; the absence of omission was the reference. The analysis focused on two complementary aspects of the evaluation of omission: quantitatively, the absolute and relative error on the CTT measured and qualitatively, the diagnostic error (a delayed transit is defined by a total CTT > 65 hours). Total and segmental CTT measured when omission occurred were greater than the reference time. The difference is particularly important, when omission occurs early during the study for all segments. Qualitative analysis showed that, for one omission of markers ingestion, a correct diagnosis of delayed colonic transit time and of the main site of delay could be obtained by the 3-compartment model in 100% of cases. For two failures of markers ingestion, "delayed" colonic transit could be regarded as normal in only 9.59% of cases; furthermore, the site of delay was correctly recognized in 83% of the cases. Despite omission of markers ingestion for one or two days, measured CTT overestimates the absolute value of colonic transit time, the formulated diagnosis (delayed transit and site of delay) is perfectly acceptable clinically.