| Indications for performing this test: Testing for serum
folate and cobalamin is done in cases presenting with chronic weight loss or chronic small
intestinal diarrhea. This is a common diagnostic tool in the assessment of small
intestinal bacterial overgrowth or suspected malabsorption.
|
|
Pathophysiology: Lesions
of the small intestinal mucosa or diseases that alter motility may negatively
affect absorption of folate and/or cobalamin. Another cause of abnormal
serum folate & cobalamin is small intestinal bacterial overgrowth
(SIBO),
which occurs
when the normal flora of the intestine overgrows and reaches pathological numbers.
SIBO may occur as a primary disturbance potentially leading to inflammatory bowel disease or secondary to intestinal disease processes such as malabsorption, inflammatory bowel disease, decreased motility, obstruction or antibiotic administration. Folate and cobalamin levels are used to establish an index of suspicion for SIBO. Although they are not very sensitive indicators of SIBO, when folate and cobalamin levels are concurrently altered as indicated above they are considered specific for the condition. As bacteria numbers increase, folate will become elevated in the serum due to increased bacterial production. At the same time, cobalamin concentration will drop because the bacteria interfere with binding of cobalamin to the intrinsic factor and inhibit absorption into circulation. Elevated folate and depressed cobalamin is fairly specific for bacterial overgrowth in animals without accompanying pancreatic disease.
Typical
views of specimens exhibiting
inflammatory bowel disease.
http://www.gicare.com/pated/eidu0001.htm
Information about Folate and Cobalamin:
Both folate and cobalamin are present in commercial pet food diets and are normally found in the serum of animals.
Folate is also produced by bacteria which make up the normal enteric microflora. It is usually found in the small intestine in its conjugated form, but prior to absorption must be hydrolyzed by a brush border enzyme. Folate is absorbed in the distal duodenum - by a carrier process at low luminal concentrations or by passive diffusion when present at high luminal concentrations .
Cobalamin is released from its carrier protein by pancreatic proteases in the proximal small intestine. Cobalamin is then transferred to the intrinsic factor supplied by the pancreas. Absorption of cobalamin takes place in the ileum through a special receptor interaction with intrinsic factor.
In cases of exocrine pancreatic insufficiency, cobalamin levels are decreased due to decreased digestive release and deficiency of pancreatic intrinsic factor. Folate levels will increase in the serum mostly likely due to increased numbers of folate producing bacteria as well as a more acidic pH, which favors absorption. Therefore, evaluation of serum folate and cobalamin is less reliable in the face of pancreatic disease.
The Test: Folate and cobalamin are measured from a
serum sample collected after a period of fasting (usually 12 hours). Normal serum
folate concentrations range from 4.7 - 9 ug/L in the dog. Normal serum cobalamin
concentrations range from 160-560 ug/L in the dog and 200-1680 ug/L in the
cat.
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http://www.spectroscopynow.com /ftp_images/2cobalamin.gif  |
| Folate | Cobalamin |
Interpretation of serum Folate and Cobalamin:
Elevated folate and decreased cobalamin: Occurs in both small intestinal bacterial overgrowth and exocrine pancreatic insufficiency.
Normal folate and decreased cobalamin: Indicates lower intestinal dysfunction such as malabsorption, increased motility, mucosal infections, and chronic inflammatory bowel disease.
Decreased folate and normal cobalamin: Indicates intestinal dysfunction of the proximal small intestine.
Decreased folate and cobalamin: Encountered with long standing intestinal disease of the entire intestine. For example, chronic inflammatory bowel disease or severe infectious processes causing diffuse malabsorbtive disorders.
Anorexia: Will cause depressed serum levels of both cobalamin and folate simply due to decreased dietary intake.
For more information...
Veterinary Laboratory Medicine. Duncan, Prasse, and Mahaffey. page 157.
Small Animal Internal Medicine. Ettinger, pages 1350, 1190-1191.
