Accuracy in assessment of colonic transit time with particles: how many markers should be used?

Background Colonic transit time (CTT) is often measured with particle methods in clinical practice, but few studies have evaluated the role of particle amounts for the results obtained. Methods Colonic transit time was studied in 28 subjects taking radiopaque particles for six consecutive days followed by an abdominal radiograph on day 7. Four distinguishable marker types were ingested simultaneously in an amount of 5, 10, 15, and 20 daily, respectively, and CTT calculated for each type as the number of retained markers divided by the daily intake. Reference values were based on 50 markers daily. Key Results Accuracy measured as median deviation of CTT from reference was for 20 markers day-1 0.08 days, for 15 markers day-1 0.10 days, for 10 markers day-1 0.12 days, and for 5 markers day-1 0.20 days. The CTT values obtained with 5 markers day-1 deviated significantly more from the reference value than CTT values obtained with 10 markers day-1 (P < 0.05) and with 15 and 20 markers day-1 (P < 0.01). Colonic transit times obtained with 20, 15, or 10 markers day-1 did not differ significantly (P > 0.1). Conclusions & Inferences Colonic transit time can be assessed with reasonable accuracy after repeated ingestion of particles. For clinical use, a daily amount of 10 or 12 markers is proposed for reporting CTT in days or hours, respectively. Doses below 10 daily yield a steeply increasing deviation from reference values.