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Memorial Sloan-Kettering Cancer Center New York, NY 10021
(In response to Question from pg. 866.)
I welcome the opportunity to respond to this question often posed by residents and clinicians. Reader be forewarned: this question lingers, decades after the inception of barium radiography, because of the lack of a relatively simple, satisfactory answer.
The definition of small-bowel transit time varies in the literature and in daily discussion, further complicating the question. Some investigators record the orocecal transit time in an upper gastrointestial and small-bowel follow-through examination, timing the small-bowel transit time from the second cup of barium [1], whereas others begin the timing from when sufficient barium fills the proximal two loops of jejunum [2]. Although barium normally enters the duodenum within 15 min of ingestion, in patients with dysmotility of the esophagus or stomach, measurement of orocecal transit time will interfere with a true measurement of small-bowel transit time. For the purist, it seems, small-bowel transit time should be measured from the moment barium enters the duodenum.
As with blood pressure measurements, "normal" comprises a range of values. Ideally, one would compare the small-bowel study in question with the patient's previous study during a period of good health to determine whether the small-bowel transit time is normal. Barring this, we must accept a range of normal and correlate the small-bowel transit time with other barium radiographic features and clinical information.
Small-bowel transit time depends on many factors including density and temperature of the barium preparation and presence of chemical additives, stress, patient age, patient positioning during the study, and the use of pharmacologic agents [1,3]. However, the most important factors, which inversely correlate with small-bowel transit time, are the volume of barium ingested and maintenance of a full stomach [1,3].
If one of the numerous pharmacologic agents advocated to shorten small-bowel transit time is used (e.g, metoclopramide), physiologic small-bowel transit time cannot be determined, and published values will not apply.
The diseases accounting for rapid small-bowel transit time (e.g., giardiasis, carcinoid syndrome, graft-versus-host disease) or prolonged small-bowel transit time (e.g., hypothyroidism, scleroderma, intestinal pseudoobstruction) are associated with clinical and radiologic features that are beyond the scope of this reply but that may be found in textbooks of gastroenterology and radiology, respectively.
Finally, for the patient reader, in the largest radiologic study of small-bowel transit time that comprised 315 normal small-bowel examinations, a mean small-bowel transit time of 84 min (range, 15 min to 5 hr) was found. In 83% (261/315) of these examinations, the small-bowel transit time was less than or equal to 2 hr, whereas 97% (304/315) reached the terminal ileum within 3 hr. Small-bowel transit time was less than 30 min in only 5% (17/315) [1]. In two other radiologic studies, comprising 87 patients, small-bowel transit time ranged from 33 to 16 min [2], and from 15 to 105 min [3].
In sum, normal barium small-bowel transit time, like normal blood pressure, must necessarily fall within a range of values published and accepted by medical experts. Most patients have a small-bowel transit time of between 30 min and 3 hr. The minority of cases, in which the small-bowel transit time lies outside of this range, should not absolutely be diagnosed as abnormal without correlation with associated radiographic and clinical findings.
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