Role of serum folate and vitamin B12 concentrations in the differentiation of small intestinal abnormalities in the dog.

Serum folate and vitamin B12 concentrations have been measured in 53 dogs presented for an investigation of malabsorption. Abnormal concentrations have permitted the differentiation of animals with small intestinal disease into three main groups, each with distinct biochemical abnormalities in the jejunal mucosa. The first group had reduced folate and vitamin B12 concentrations. Jejunal biopsies revealed marked villous atrophy and generalised biochemical abnormalities in the brush borders, lysosomes and endoplasmic reticulum. The second group had reduced folate but normal vitamin B12 concentrations and although histological changes were minimal there were specific biochemical changes confined to the brush borders. In the third group, increased folate and reduced vitamin B12 concentrations suggested a bacterial overgrowth in the proximal small intestine. Minor histological changes were accompanied by marked biochemical changes in brush borders and lysosomes. A group of animals with severe exocrine pancreatic insufficiency had increased mean folate but reduced mean vitamin B12 concentrations. These changes are consistent with bacterial overgrowth, but could be due to defective degradation of a B12-binding protein.