We studied radiolabeled fecal
bile acid excretion in 11 normal subjects and 17 patients with idiopathic chronic
diarrhea for three major purposes: to establish normal values for this test in the presence of increased stool volumes (induced in normal subjects by ingestion of poorly absorbable solutions); to test for
bile acid malabsorption in the patients and to correlate this with an independent test of ileal function, the Schilling test; and to compare the results of the
bile acid excretion test with the subsequent effect of a
bile acid binding agent (
cholestyramine) on stool weight. In normal subjects fecal excretion of the radiolabel was increased with increasing stool volumes. As a group, patients with idiopathic chronic
diarrhea excreted radiolabeled
bile acid more rapidly than normal subjects with induced
diarrhea (t1/2 56 +/- 8 vs. 236 +/- 60 h, respectively, p less than 0.005). There was a statistically significant positive correlation between t1/2 of radiolabeled
bile acid and Schilling test results in these patients. Although 14 of 17 patients absorbed labeled
taurocholic acid less well than any of the normal subjects with comparable volumes of induced
diarrhea,
cholestyramine had no statistically significant effect on stool weight in the patient group, and in none of the patients was stool weight reduced to within the normal range. In summary, most patients with idiopathic chronic
diarrhea have
bile acid malabsorption (as measured by fecal excretion of labeled
bile acid), but they do not respond to
cholestyramine therapy with a significant reduction in stool weight. Although the significance of these findings was not clearly established, the most likely interpretation is that
bile acid malabsorption is a manifestation of an underlying intestinal motility or absorptive defect rather than the primary cause of
diarrhea.