Page 441 - Small Animal Internal Medicine, 6th Edition

CHAPTER 27 Diagnostic Tests for the Alimentary Tract 413

lymphangiectasia, gastrointestinal (GI) blood loss, severe feces to a laboratory familiar with this coccidium and is able
infiltrative alimentary tract disease, parvoviral diarrhea, or to perform special procedures to detect it. Enzyme-linked
VetBooks.ir ascites. It is important to measure the serum albumin using immunosorbent assay (ELISA), polymerase chain reaction
(PCR), and indirect fluorescent antibody (IFA) methodolo-
technology designed for canine and feline albumin; some
techniques used for measuring human albumin produce
tosporidia (see later).
falsely low measurements of canine albumin. It is important gies are more sensitive than fecal flotation for finding cryp-
to use the same lab when repeating the serum albumin con- Direct fecal examination, although convenient, is not sen-
centration; different labs often have slightly different normal sitive for nematodes and should not replace flotation tech-
ranges, which causes confusion when monitoring hypoalbu- niques. However, occasionally amebiasis, strongyloidiasis,
minemic patients. and whipworm infections missed by flotation procedures
Ill animals (especially those receiving multiple drugs) are can be detected by direct examination. Motile Giardia and
at risk for secondary renal or hepatic failure. Very young and Tritrichomonas trophozoites may be found if the feces are
very small animals easily become hypoglycemic if they very fresh and the smear is adequately diluted with saline
cannot eat or absorb ingested nutrients. Finding hypercalce- solution. Direct examination is much less sensitive than zinc
mia or hypoalbuminemia may provide a clue to the underly- sulfate flotation, IFA, PCR, and ELISA techniques in detect-
ing problem in animals with weight loss or hyporexia. ing giardiasis (see later).
Fecal sedimentation is time consuming and offers no
SERUM CORTISOL advantage in detecting common GI tract parasites. However,
Atypical hypoadrenocorticism is more common in dogs it does detect fluke ova missed by other techniques, espe-
than many clinicians realize. Measuring resting serum cor- cially the ova of Eurytrema spp., Platynosomum spp., Amphi-
tisol as a screening test to decide whether or not to perform merus spp., and Heterobilharzia spp.
an ACTH-stimulation test has become standard practice in Feces may be preserved by mixing equal volumes of feces
patients with difficult to diagnose/control vomiting, diar- and 10% neutral buffered formalin or by using commercially
rhea, or hyporexia. available kits. Polyvinyl alcohol is used in the latter, and feces
preserved in this manner can be examined weeks to months
URINALYSIS later. These techniques are especially useful if one cannot
Urinalysis is required to accurately evaluate renal function immediately examine feces for protozoal cysts.
and, in conjunction with the urine protein/creatinine ratio, PCR analysis on feces can detect Heterobilharzia spp. (GI
to help determine the cause of hypoalbuminemia. Urine Lab, Texas A&M University, College Station, TX). It appears
should always be obtained before fluid therapy is begun. to be at least as sensitive as fecal sedimentation.

FECAL PARASITIC EVALUATION FECAL DIGESTION TESTS

Fecal flotation is indicated in most animals with alimentary Examining feces for undigested food particles by staining
tract disease or weight loss, especially puppies and kittens. thin fecal smears with the Sudan stain (for fat) or iodine (for
Even if parasitism is not the primary problem, it may cause starch and muscle fibers) is discouraged. Finding excessive
additional debilitation. Concentrated salt or sugar solutions amounts of undigested fecal fat is supposedly suggestive of
are typically used for fecal flotation. The former are usually exocrine pancreatic insufficiency (EPI), but this test has
superior, although incorrectly made solutions may not force many false-positive and false-negative results. If EPI is a dif-
heavier ova (e.g., whipworms) to float. Moreover, concen- ferential diagnosis, a species-specific serum trypsin-like
trated salt solutions can distort Giardia cysts, making iden- immunoreactivity (TLI) is the recommended test (see the
tification difficult. Zinc sulfate flotation solution is preferred section on digestion and absorption tests).
for detecting nematode ova and Giardia cysts. Centrifuga- Fecal analysis for proteolytic activity (i.e., the fecal trypsin
tion promotes separation of cysts from the fecal matter and content) also tests for EPI. Qualitative estimates (e.g., fecal
results in a more sensitive fecal examination. Some parasites film digestion, fecal gelatin digestion) are unreliable. Quan-
intermittently shed small numbers of ova or cysts, necessitat- titative analysis is seldom needed because the TLI test is
ing repeated fecal analyses for diagnosis. Whipworm and easier to perform. It is rarely necessary to quantitate fecal
Giardia infections can be especially difficult to diagnose with proteolytic activity to diagnose EPI caused by pancreatic
fecal flotation. duct obstruction (exceedingly rare), something TLI does not
The ova of the most common tapeworm species are con- detect. In this test, feces are collected for 3 consecutive days
tained in segments and are not found by flotation techniques. and stored frozen until sent to the laboratory. Quantitated
Nanophyetus salmincola (the fluke that transmits salmon fecal fat analysis is almost never indicated.
poisoning) is detected by many flotation solutions, although Fecal occult blood analyses are seldom useful because
sedimentation examinations are required to detect most most pets eat meat by-products that cause a positive reac-
other fluke ova. Cryptosporidiosis is difficult to detect by tion. False-positive reactions may also be produced by
routine flotation techniques. The clinician should send the cimetidine, oral iron preparations, and some vegetables. The