The Sitz marker study is an older technique to estimate colonic transit time.
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.
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
- 1. Lin HC, Prather C, Fisher RS et-al. Measurement of gastrointestinal transit. Dig. Dis. Sci. 2005;50 (6): 989-1004. Pubmed citation
- 2. Southwell BR, Clarke MC, Sutcliffe J et-al. Colonic transit studies: normal values for adults and children with comparison of radiological and scintigraphic methods. Pediatr. Surg. Int. 2009;25 (7): 559-72. doi:10.1007/s00383-009-2387-x - Pubmed citation