Specific diagnostic tests
A diagnosis of EPI is most reliably based on clinical signs and pancreatic function test results. The gold standard for diagnosing
EPI in people is in vitro analysis of pancreatic secretions obtained from the duodenum following stimulation by cholecystokinin
and secretin.15 This technique has proved to be difficult and impractical in dogs.16 The recommended test for diagnosing EPI in dogs is the canine serum trypsin-like immunoreactivity (cTLI) by radioimmunoassay.
Canine serum trypsin-like immunoreactivity. This test measures the trypsinogen that has entered the bloodstream directly from the pancreas. Enzymes that originated or
were activated within the intestinal lumen are not measured, which eliminates any interference by intestinal inflammation.2 The test is also not affected by exogenous sources of pancreatic enzymes because it is species-specific.16 The reference range for cTLI is 5.7 to 45.2 µg/L, with values below 2.5 µg/L being highly diagnostic for EPI when concurrent
clinical signs exist.2
Although not affected by intestinal inflammation, the cTLI test may be affected by pancreatic inflammation.6,17 Pancreatitis affecting any residual functioning acinar cells may falsely elevate cTLI concentrations.17 Dogs with EPI may have normal cTLI concentrations in the presence of kidney disease because trypsinogen is renally excreted.2,18 The cTLI concentrations could be normal in animals with EPI secondary to pancreatic duct obstruction.16 Postprandial samples may also result in falsely elevated cTLI results.2,18 Thus, the sample should be obtained in a patient that has been fasted for 12 to 18 hours, and the sample should be nonhemolyzed.
Despite these potential interferences, the cTLI test is considered 100% sensitive and specific for EPI with results below
1.9 µg/L.16
Canine TLI testing by radioimmunoassay is available through commercial laboratories such as the Texas A&M University College
of Veterinary Medicine's Gastrointestinal Laboratory, Antech Diagnostic Laboratory, or Idexx Laboratories. An in-house ELISA
test kit to detect cTLI has been investigated.19
Serum pancreatic lipase immunoreactivity. Serum pancreatic lipase immunoreactivity (PLI), used to detect pancreatitis, is also a sensitive test for diagnosing EPI.
Unfortunately, poor specificity makes it inferior to the cTLI test for this purpose.20 The newest version of the PLI test, the Spec cPL Test (Idexx Laboratories), has been optimized for diagnosing pancreatitis
but may not be useful for diagnosing EPI. In general, all available forms of pancreatic lipase testing should be used for
diagnosing pancreatitis rather than pancreatic insufficiency.
Fecal pancreatic elastase 1. Fecal pancreatic elastase 1 is a zymogen produced exclusively within pancreatic acinar cells.21 It survives intestinal transit unchanged and is unaffected by intestinal inflammation.21 An ELISA test for fecal pancreatic elastase 1 (Elastase 1 Canine—ScheBo Biotech AG) in dogs is available and is marketed
as a screening tool for EPI. A fecal pancreatic elastase 1 value < 10 µg/g feces indicates a diagnosis of EPI. Values > 40
µg/g feces indicate normal exocrine pancreatic function, while values between 10 and 40 µg/g feces are borderline results.
In borderline cases, further testing is recommended.22 This test is species-specific, so it is unaffected by pancreatic enzyme supplementation. Fecal pancreatic elastase 1 measurement
has been used extensively in diagnosing EPI in people.21
Other tests. Several tests for EPI have been rendered nearly obsolete by the advent of the cTLI test. These include tests
for fecal proteolytic activity, which should be low in dogs with EPI, including the x-ray film method, the azocasein method,
and the radial enzyme diffusion method.2,16 The bentiromide test, also known as the serum n-benzoyl-L-tyrosine-p-aminobenzoic acid test (BT-PABA), is an indirect method of assessing the presence of chymotrypsin in the blood.16-18,23
Other tests that are no longer actively used include the starch tolerance test, the D-xylose absorption test, and the oral
fat absorption test.21 None of these tests are as sensitive and specific as the cTLI test for diagnosing EPI.
|
Featuring Information from:
