Figure 57-10.

Diagram of the absorption of folate and cobalamin.

In diseased intestine, proximal and distal mucosal damage causes folate and cobalamin malabsorption, respectively. Reduced serum folate and/or cobalamin are markers for proximal and/or distal SI damage. Classically, small intestinal bacterial overgrowth (SIBO) causes increased folate uptake because of bacterial folate synthesis and decreased cobalamin uptake because of bacterial incorporation. However, these changes are poorly sensitive, and cannot be used to reliably diagnose SIBO: they do not correlate with antibiotic responsiveness. IF, Intrinsic factor.

(From Ettinger SJ, Feldman EC, editors: Textbook of Veterinary Internal Medicine, ed 7, Philadelphia, 2010, Saunders, p 1528.)