Vitamin B12 deficiency following restorative proctocolectomy

Restorative proctocolectomy (RP) involves terminal ileal resection and formation of a small bowel reservoir that predisposes to bacterial overgrowth. It was anticipated that these patients would be at risk of vitamin B12 deficiency.

Vitamin B12 levels were measured sequentially in 171 patients who underwent RP. Prospective results were obtained from all 20 patients undergoing pouch formation after the commencement of the study. Further results were obtained retrospectively from case notes and computerized laboratory records of the 151 patients who underwent RP prior to the commencement of the study and these were correlated with the results of follow-up samples taken prospectively from the same patients after the commencement of the study. The median age of the patients was 40 years (range: 13-67) and the median duration of follow up was 5.4 years (range: 1-12). Patients with an abnormally low serum B12 level underwent both a Schilling and a hydrogen breath test. Eight of these patients were then treated with oral vitamin B12.

Abnormally low serum B12 levels were found in 25% of patients. Forty per cent of our patient group had three or more sequential B12 measurements and of these, 66% showed steadily declining B12 levels. Ninety-four per cent of patients with low B12 had a normal Schilling test and were negative for bacterial overgrowth.

Subnormal vitamin B12 levels develop in almost one-quarter of patients after pouch surgery. The exact mechanism for B12 deficiency in these patients is uncertain. In the majority of patients undergoing RP, vitamin B12 levels fall on sequential measurement. Serum B12 levels should be measured during follow up and pouch patients with subnormal B12 levels, should see them successfully restored to a normal value after treatment with oral B12 replacement therapy.