Fecal Analysis (maldigestion)

Indications for performing this test:

Fecal analysis is the direct microscopic evaluation of feces for fat, starch or undigested muscle fibers. Various stains can be used to identify these materials in feces depending on which substrate one is trying to identify. Feces can also be tested for fecal proteolytic activity, which is a reflection of the pancreas’ ability to produce protease enzymes.

At one time, these tests were used frequently in the diagnosis of maldigestion syndromes such as Exocrine Pancreatic Insufficiency (EPI). For the most part, they are now considered unnecessary due to the development of the Trypsin-Like Immunoreactivity (TLI) test.

Canine Juvenile Pancreatic Atrophy is a clinical syndrome in which the onset of PAA (and EPI) usually occurs from 6 months to one year of age. It is reportedly more common in German shepherd dogs and is thought to have a hereditary link.

· These tests are relatively easy to perform and are inexpensive, however, they have poor sensitivity for EPI and suffer from subjectivity and lack of standardization. These tests are imprecise and interpretation is difficult due to the variation in fecal characteristics influenced by diet and intestinal transit time.

· “Microscopic examination of feces for undigested food, assessment of fecal proteolytic activity using x-ray film gelatin digestion, starch tolerance, plasma turbidity, and glucose tolerance are all unreliable and have limited value given the availability of more sensitive and specific tests.” D.A Williams (Developer of the TLI) in S. Ettinger’s Textbook of Veterinary Internal Medicine.

The Tests:

Fecal fat analysis can be done by several methods, looking for either digested fats or undigested fats. Briefly, fresh feces is mixed with the Sudan III or IV stain and a smear is prepared on a microscope slide. Under the microscope, undigested or "neutral" fats appear as orange globules, which when increased are indicative of maldigestion. The digested fats are not observed. When feces, Sudan stain, and 36% acetic acid are smeared on a slide and boiled, the "split" fats that have been digested but not absorbed will re-associate. Microscopically, these appear as orange globules (increased numbers indicate malabsorption if neutral fats are within normal limits).

The amount of fats or fatty acids present is influenced by diet, so feces from a control animal on the same diet should be assessed along with the patient. Usually <5 globules/HPF are considered normal.

Fecal starch analysis is performed with a 2% Lugol’s iodine stain. Undigested starch granules appear as dark blue-black granules on microscopic evaluation. Under normal circumstances, rare (0-5) granules/HPF are visualized; this number will increase with EPI.

Fecal protein: To identify undigested muscle fibers, one can prepare an unstained slide or mix feces with Lugol’s or Wright’s stain. Upon microscopic evaluation, undigested muscle fibers appears as blunt-ended cross-striations, which are not normally seen in feces. The presence of these fibers in the feces of animals on a meat diet suggests EPI.

Fecal proteolytic activity was measured historically based on the ability of a fecal suspension to remove the gelatin emulsion from X-ray film.