Page 618 - Clinical Small Animal Internal Medicine

586 Section 6 Gastrointestinal Disease

secretion of trypsin and trypsinogen is normal and concentrations. The same is true for cats with concur-
VetBooks.ir therefore serum TLI concentrations are also normal. rently increased serum feline pancreatic lipase (fPLI,
Spec‐fPL) concentrations indicating pancreatitis.
In these cases, the diagnosis of EPI is quite challenging.
Trypsin‐like immunoreactivity testing can be per-
The current assays for the measurement of pancreatic
lipase concentration (i.e., Spec‐cPL) are not suitable for formed in animals that are already on enzyme supple-
the accurate measurement of pancreatic lipase concen- mentation without this affecting the results. TLI assays
trations at very low concentrations, and therefore iso- are species specific and do not measure trypsinogen and
lated pancreatic lipase deficiency cannot be diagnosed trypsin of other species.
using these assays. Although epidemiologic studies are
lacking, isolated pancreatic lipase deficiency in dogs is Pancreatic Fecal Elastase
considered to be an uncommon cause of EPI.
Single TLI results within the equivocal range (usually An ELISA for the measurement of pancreatic elastase in
between 2.5 and 5.7 μg/L) in dogs with clinical signs of feces is commercially available and is marketed in Europe
gastrointestinal disease need to be interpreted with (Shebo Biotech, Germany) for the diagnosis of canine
caution. In these patients, subsequent retesting of serum EPI. It is considered to be specific for EPI, although a
TLI may show either a normal concentration or progres- recent study reported false‐positive results in 23.1% of
sion to EPI. Therefore, patients with canine TLI (cTLI) cases and the sensitivity of this test has not been suffi-
results in the equivocal range should be investigated for ciently evaluated. The fact that this test is easy and quick
chronic intestinal disease, while cTLI concentrations to perform might make it a reasonable initial approach
should also be measured a few weeks later. for dogs with suspected EPI, but a positive test result
Some dogs with no clinical signs characteristic of EPI must be verified by measurement of a serum TLI con-
have repeatedly subnormal (<5.7 μg/L) cTLI concentra- centration. This test might also be useful for EPI cases
tions. These dogs have been shown to have subclinical that are due to pancreatic duct obstruction. However, to
EPI and some, but not all, are expected to develop clini- date such cases have only been anecdotally reported in
cal EPI in the future. The time of progression from the the veterinary literature.
subclinical to the clinical disease varies greatly and
might be from a few months to years. Thus, these Other Tests
patients should be closely monitored for the develop-
ment of clinical signs of EPI and cTLI testing should be Serum amylase and lipase activities have been shown to
repeated periodically. It should be noted that a single have no value in the diagnosis of EPI in either dogs or
serum cTLI concentration is not sufficient for diagnos- cats. Canine pancreatic lipase immunoreactivity concen-
ing subclinical EPI. trations are low or undetectable in most dogs with EPI,
Because renal disease might increase serum cTLI con- but commercial assays for the measurement of serum
centrations and obscure a diagnosis of EPI, reevaluation PLI concentration (Spec‐cPL and Spec‐fPL) are not use-
of nondiagnostic serum cTLI concentrations in azotemic ful for the diagnosis of EPI in dogs and cats, respectively,
dogs suspected of having EPI is recommended. Similarly, because they have been optimized to detect changes in
concurrent pancreatitis might falsely increase the serum the higher levels of their respective working ranges.
cTLI concentration. Measurement of the fecal proteolytic activity has been
Due to the fact that EPI appears to be less common in used in the past for the diagnosis of EPI in dogs and cats.
cats than in dogs, diagnosis of this disease has been less A plethora of other tests, including microscopic exami-
well investigated and is more challenging in this species. nation of feces and the bentiromide absorption (BT‐
Similar to dogs, the feline TLI (fTLI) test appears to be PABA) test, have also been used for the diagnosis of EPI.
the most reliable test for the diagnosis of EPI in cats with These tests often give false‐positive and/or false‐nega-
a specificity of at least 85%. The sensitivity of this assay tive results, and many of them are impractical, expensive
for the diagnosis of feline EPI has not been evaluated or of limited availability, and thus are not recommended
to date. Although there are currently two assays that for the diagnosis of canine or feline EPI. However, these
measure fTLI in serum (one radioimmunoassay that is tests may be useful in special cases where serum TLI
available in the USA and one ELISA available in Europe), concentration is in the normal range (e.g., EPI due to
only one of those assays (the radioimmunoassay) has pancreatic duct obstruction) but EPI is heavily suspected
been reported to be analytically validated; this test is based on the clinical picture.
available through the Gastrointestinal Laboratory at
Texas A&M University. Similar to dogs, it can be recom- Histopathology
mended that nondiagnostic serum fTLI concentrations
in azotemic cats suspected of having EPI be reevaluated, Exocrine pancreative insufficiency is a functional and
because renal disease might falsely increase serum fTLI not a histopathologic diagnosis, and thus histopathology