Colonic transit study
The colonic transit study is an older technique to estimate colonic transit time.
Various names are used for this type of study including shapes study, colon motility test, Sitz marker study and Transit-Pelletsmethod, and variations thereof.
In constipation, it can help distinguish between slow colonic transit and a defecation disorder.
The patient ingests a number of radiopaque markers (plastic rings containing radiopaque material) in a meal and abdominal radiographs are obtained to monitor the clearance of the rings from the colon.
Normal colonic transit time is 20-56 hours, and most adults will clear all the markers in 4-5 days.
Laxatives (and possibly GI-active medications) should be temporarily discontinued, otherwise, no special preparation is needed. At times due to obstipation patients are unwilling to stop their purgatives in which case the study may be done with them.
Three main techniques are used:
- 20 or 24 markers are ingested in a single dose, and then serial daily abdominal radiographs are obtained (more common)
- 20 or 24 markers are ingested and a single abdominal radiograph is obtained six days later
- 10 markers are ingested every day for three days and an abdominal radiograph is obtained on days four, seven, and ten
Most define <20% of the original rings at five days as normal. For instance, if 24 rings are used, then <5 rings should be present in five days.
If using 20 rings and daily radiographs, some use the schedule:
- day 1: ≤16 rings
- day 2: ≤8 rings
- day 3: ≤4 rings
- day 4: ≤2 rings
- day 5: ≤1 ring