Serum methylmalonic acid and total homocysteine in patients with suspected cobalamin deficiency: A clinical study based on gastrointestinal histopathological findings

We compared the sensitivity and specificity of the two metabolite tests, methylmalonic acid (MMA) and total homocysteine (Hcy) in serum, and serum cobalamin (Cbl) in patients referred to our hospital because of suspected cobalamin deficiency and a serum cobalamin value at the referring unit <200 pmol/L. All 111 patients included were investigated using upper gastrointestinal endoscopy with biopsy specimens taken from the gastric and duodenal mucosa to find a morphological basis for cobalamin malabsorption as well as the Schilling test for the validation of the serum tests. All patients were treated with cobalamin and new blood samples were taken after 4 weeks. We found no difference in sensitivity and specificity between serum MMA, Hcy, and Cbl in identifying patients with and without conditions compatible with cobalamin malabsorption. Elevated serum MMA and Hcy were also found in about 15% of the group of patients with normal Schilling tests and without a morphological basis for cobalamin malabsorption. Moreover, most patients in this group responded with decreased values of the metabolite tests following cobalamin treatment, suggesting that neither elevated metabolites nor a decrease in these values following cobalamin treatment are specific for cobalamin deficiency.