Stool Burden Is a Reliable Marker of Slow Colonic Transit in Adults

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Plain-film abdominal X-rays are often used in the work-up of chronic constipation because stool burden is easily visible. They're noninvasive, relatively inexpensive and pose a low radiation risk.

Some research suggests, though, that X-rays have limited value for diagnosis of slow transit constipation. The principal problem is poor interobserver agreement among the various methods of grading stool burden. Of those, the Leech method has been demonstrated to have the highest reproducibility and interobserver agreement, but it was developed for use in pediatric patients.

A separate problem in assessing colonic transit is that Sitzmarks capsules—a commonly used type of radiopaque marker—are widely unavailable because of manufacturing problems.

David J. Cangemi, MD, of the Mayo Clinic, Kyle Staller, MD, MPH, director of the Gastrointestinal Motility Laboratory and a gastroenterologist in the Division of Gastroenterology at Massachusetts General Hospital, and colleagues investigated whether scoring stool burden on X-rays by the Leech method could be an alternative way to assess colonic transit. Their work is published in the American Journal of Gastroenterology.

Study Details

The research team retrospectively studied a "real world" cohort of 361 adults with chronic constipation who underwent a five-day radiopaque marker (ROM) transit study at Mass General or one of its partner hospitals between October 2012 and September 2017. All but 20 of the patients had balloon expulsion testing with anorectal manometry.

An abdominal X-ray was obtained five days after ingestion of 24 radiopaque markers in a Sitzmarks capsule. Slow colonic transit was defined as five or more markers being visible on the X-ray.

As a comparison, two researchers independently graded the stool burden on abdominal X-rays on day 5. Following the Leech method, they drew a vertical line upward from the fifth lumbar vertebrae, another line to the left pelvic brim, and a third line to the right anterior superior iliac crest. They scored stool burden in the right colon, left colon and rectosigmoid colon from 0 (no feces visible) to 5 (severe fecal loading with bowel dilation).

Motility Testing Results

40% of the patients had slow transit constipation as determined by the ROM transit study. Of the 341 patients who underwent anorectal manometry:

• 39% had neither slow transit constipation nor outlet obstruction
• 22% had slow transit constipation only
• 21% had outlet obstruction only
• 18% had both outlet obstruction and slow transit constipation

Leech Method Utility

The average stool burden score was significantly higher in patients with slow transit constipation than in those with normal transit:

• Grader 1 — 8.1 vs. 6.9; P < .0001
• Grader 2 — 8.5 vs. 5.8; P < .0001

There was a strong correlation between the stool burden scores assigned by the two observers.

There was moderate to strong correlation between the stool burden score and the number of remaining radiopaque markers.

For both graders, the ideal cutoff between high and low stool burden was a score of 7.

Clinical Utility

At a time when Sitzmarks capsules are widely unavailable, determining colonic transit by scoring stool burden on abdominal X-rays may be a useful alternative for colonic transit evaluation, particularly when using the Leech method. Patients should discontinue laxatives and opioids five days before the X-ray.

Stool burden scores may vary between observers. Ideally, clinicians should first evaluate a number of abdominal X-rays against the results of radiopaque marker studies to determine their ideal cutoff score for future stool burden grading.

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