Vitamin B12 absorption after ileorectal anastomosis for Crohn's disease: effect of ileal resection and time span after surgery.

OBJECTIVE

To examine the impact of ileorectal anastomosis on vitamin B12 absorption, as measured by the Schilling test, in patients with Crohn's disease.

PATIENTS

Eighty-two patients with Crohn's disease who had undergone ileorectal anastomosis.

METHODS

Of the 82 patients with Crohn's disease and ileorectal anastomosis, 75 had their absorption of vitamin B12 tested using the Schilling test at least once while their first ileorectal anastomosis was functioning, corresponding to 605 years of observation.

RESULTS

An ileal resection of more than 60 cm invariably resulted in decreased vitamin B12 absorption. In patients who had less than 60 cm of their ileum resected 53% had test results, indicating that vitamin B12 was malabsorbed. The extent of malabsorption did not correlate with the length of ileal loss in this subgroup of patients (r = -0.26; P = 0.053). Even resections of 10 cm or less were associated with malabsorption in 38% of patients. This suggests that factors other than the remaining ileal length are important for vitamin B12 absorption in Crohn's disease patients with ileorectal anastomosis. An improvement in vitamin B12 absorption over the years was not observed in the 35 patients in whom the test was repeated, and intraindividual Schilling test results fluctuated between pathological and normal values in several patients.

CONCLUSIONS

Most Crohn's disease patients with ileorectal anastomosis have vitamin B12 malabsorption. Individuals with more than 60 cm of ileal loss are particularly affected and testing for malabsorption appears superfluous in this group. Approximately 50% of the patients with resections of 60 cm or less malabsorbed vitamin B12, but it was not possible to predict which patients should receive vitamin B12 substitutes based on the length of the remaining ileum alone. However, it may also be difficult to make a rational therapeutic decision based on the results of the Schilling test, because the test shifted between normal and pathological values over time in many of the patients studied.