Sensitivity and Specificity in Tests of Distal Ileal Function: Prospective Comparison of Bile Acid and Vitamin B12 Absorption in Ileal Resection Patients

Abstract

Abstract Bile acid and vitamin B 12 absorption were compared prospectively in 22 patients with distal ileal resection, 7 with similar diarrhea but apparently normal ileal function, 5 with the stagnant loop syndrome, and 3 with steatorrhea due to digestive abnormalities. Also studied were 18 healthy control subjects. A test meal containing glycine- 14 C-labeled glycocholate, 3 H-ring-labeled taurocholate, vitamin B 12 - 57 Co with intrinsic factor, and 51 CrCl 3 as nonabsorbable marker was administered to fasting patients. Bile acid absorption was assessed by appearance of 14 CO 2 in breath and by fecal excretion of 14 C or 3 H; B 12 absorption was measured by excretion of 57 Co in urine (Schilling test). Based on fecal excretion of 3 H, nearly all patients with ileal resection had unequivocal bile acid malabsorption. Measurement of 14 CO 2 in breath was less sensitive since four false negatives were identified. Measurement of both 14 CO 2 and fecal 14 C was as sensitive as measurement of fecal 3 H. Of the 14 patients with resections less than 100 cm, 4 had normal Schilling tests, despite nearly all having bile acid malabsorption; both tests were equivocal or abnormal in patients with larger resections. In patients with similar diarrhea but no evidence of ileal dysfunction, bile acid malabsorption was not present, since the ratio of fecal bile acid radioactivity to marker radioactivity was significantly smaller than in patients with ileal resection; B 12 absorption was normal. The breath test appears to be a useful screening test for the detection of the stagnant loop syndrome. Its interpretation is uncertain in patients with ileal dysfunction, since such patients may also have bile acid malabsorption. Thus, the clinical value of the breath test or measurement of bile acid absorption in such patients probably can only be determined by future studies which relate test results to therapeutic response.