Page 451 - Small Animal Internal Medicine, 6th Edition

CHAPTER 27 Diagnostic Tests for the Alimentary Tract 423

contrast has reached the colon. If chemical restraint is abso- and warm, sterile physiologic saline solution (20 mL/kg) is
lutely necessary, acetylpromazine may be used. Fluoroscopy administered rapidly. The abdomen is massaged vigorously
VetBooks.ir is rarely needed for these studies. for 1 to 2 minutes, and then some of the fluid is aspirated.
Hypertonic iodinated contrast agents are inferior to
The aspirate is evaluated cytologically.
barium for small intestinal studies because they decrease the
intestinal transit time and can cause considerable fluid shifts
by osmotically drawing fluid into the GI tract. Their poten- DIGESTION AND ABSORPTION TESTS
tial advantages rarely outweigh their disadvantages. Isotonic
iodinated contrast agents are safer and produce better detail Exocrine pancreatic function may be tested by measuring
than the hypertonic iodinated compounds but are still less fecal proteolytic activity (not recommended), fat absorption
diagnostic than barium. with and without pancreatic enzymes (not recommended),
or serum TLI (recommended).
Findings Serum TLI is the most sensitive and specific test for EPI
In a complete intestinal obstruction, the barium column and is convenient (i.e., submit 1 mL of refrigerated serum
cannot advance beyond a certain point, and the intestines obtained after an overnight fast) and readily available. The
orad to this point are typically dilated. A partial obstruction TLI assay detects circulating proteins produced by a nor-
may be denoted by delayed passage past a certain point mally functioning exocrine pancreas and is even valid in
(there may or may not be dilation of the intestines orad to animals receiving pancreatic enzyme supplements orally. It
this point) or constriction of the lumen. Because it is easy to is important to use an assay that is specifically designed for
overinterpret contrast-enhanced radiographs of the intes- the species being tested. Pancreatitis, renal failure, and severe
tines, changes must be seen on at least two different films malnutrition may increase the serum TLI concentrations,
taken at different times before a disease is diagnosed. but this rarely causes results to be misinterpreted. However,
“Enteritis” is often incorrectly diagnosed if a fine “brush if EPI is caused by obstruction of the pancreatic ducts (rare)
border” in the lumen is found. However, this finding actually as opposed to acinar cell atrophy or destruction (common),
results from the barium normally distributing itself among the serum TLI test may not detect maldigestion. In such
villi, not from enteritis. Infiltration from neoplasia or inflam- cases, a quantitative fecal proteolytic assay is required.
matory infiltrates classically causes scalloped margins (some- Normal dogs have serum TLI activities of 5.2 to 35 µg/L.
times called thumb-printing). However, its absence does not Values of less than 2.5 µg/L confirm a diagnosis of EPI.
rule out infiltrative disease. Focal dilations not caused by Values between 2.5 to 5.2 ug/L should be rechecked later.
obstruction (i.e., diverticula) are rare and usually represent Normal cats have higher values (28-115 µg/L). The serum
a localized neoplastic infiltrate. In rare instances, unsus- TLI assay is primarily indicated in patients with chronic
pected intestinal blind loops or short-bowel syndromes may small intestinal diarrhea or chronic weight loss of unknown
be detected. Motility problems may cause slowed passage of origin. Feline EPI is less common than canine EPI, but the
the contrast through the alimentary tract, but hypomotility test is still a good idea in cats. Although principally used to
is usually due to obstruction or abdominal inflammation. detect EPI, serum TLI values substantially greater than
normal are suggestive of pancreatitis.
INDICATIONS FOR BARIUM
CONTRAST ENEMAS
This is a largely outdated procedure that is almost never done SERUM CONCENTRATIONS
anymore. It might be useful if there is a severe colonic lesion OF VITAMINS
and ultrasound and colonoscopy are not available. The
reader is referred to earlier editions of this text for more Serum concentrations of cobalamin and folate are some-
information on barium contrast enhanced enemas. times helpful in animals with chronic small intestinal diar-
rhea or chronic weight loss. These tests may provide evidence
of severe small intestinal mucosal disease; however, they are
PERITONEAL FLUID ANALYSIS insensitive for small intestinal disease and not specific for
any particular intestinal disease. Dietary cobalamin is
Fluid analysis is discussed in detail in Chapter 34. The fluid absorbed in the intestine, principally the ileum; hence, ileal
is obtained by performing abdominocentesis with a syringe disease is thought to be particularly likely to cause hypoco-
and needle. If this technique fails, a multifenestrated catheter balaminemia ostensibly because of malabsorption of the
(e.g., dialysis catheter) may be successful. It is sometimes vitamin. Cobalamin concentrations are usually decreased in
best to allow fluid to spontaneously drain out of the catheter dogs with EPI, possibly because of the abnormalities in small
without applying negative pressure. intestinal bacterial populations in such animals. Severe
If peritoneal inflammation is suspected but abdominal mucosal disease, especially in the region of the ileum, may
fluid cannot be retrieved, a diagnostic peritoneal lavage may also cause serum cobalamin concentrations to be decreased.
be performed. In this method a sterile catheter (preferably Perhaps the major indications for measuring serum cobala-
with multiple fenestrations) is inserted into the abdomen min are to look for evidence of intestinal disease in patients