Page 465 - Problem-Based Feline Medicine

22 – THE CAT WITH ABDOMINAL DISTENTION OR ABDOMINAL FLUID 457

A complete blood count may reveal a mature neutro- of 1 was reported to have a negative predictive value
philia (chronic inflammation), lymphopenia (stress), of 91% (and a higher ratio would presumably have a
and high plasma total protein (increased globulins and higher negative predictive value.)
fibrinogen). – Rivalta’s test is useful to confirm that the fluid is
an exudate, by testing for coagulation of protein
A serum chemistry profile may reveal hyperglobuline-
in an acetic acid solution. Five ml of distilled
mia and a decreased albumin to globulin ratio. (Total
water and one drop of 98% (glacial) acetic acid
serum protein is less than plasma protein because of the
are mixed in a test tube. Vinegar should be a
absence of fibrinogen.) Liver enzymes ± bilirubin will
practical alternative to use as a point-of-care test.
be elevated if there is hepatic involvement.
One drop of the effusion is carefully layered on
“FIP tests”, which include various serum antibody the surface of the solution. If the drop disappears
tests and RT-PCR assays for FCoV viral antigens, and the solution remains clear, the test is nega-
are often non-contributory. Positive tests indicate tive and the fluid is a transudate. If the drop
exposure or presence of FCoV and not necessarily the retains its shape, remains on the surface, or
FIP strains. Tests are likely to be positive with classic slowly floats down, the test is positive and the
effusive FIP, but a negative test result does not rule out fluid is an exudate. Rivalta’s test may also be
the disease if the clinical, laboratory and pathologic positive in septic peritonitis and lymphoma (i.e.
findings are typical of the disease. Cats with very high other causes of exudates), but these disorders
titers are likely to have FIP. Furthermore, because the can usually be ruled in or out with other tests.
negative predictive value of the antibody test is high – Glucose may be detected with a urine dipstick but
overall, cats with abdominal effusion and a negative the diagnostic value of glucose level is not known.
antibody test result are unlikely to have FIP (although – Direct immunofluorescence of FCoV antigen
serum antibody titers may be low because of binding by in the peritoneal fluid macrophages. This has
the large viral load in the effusion). been reported to have a specificity and positive
predictive value of 100%, and negative predic-
Abdominal radiography or ultrasonography will
tive value of 57–89%.
demonstrate peritoneal fluid, typically containing
– Utility of measuring FCoV antibody in the
echogenic debris.
effusion varies, but it is at least as good as, and
Abdominocentesis. Cytologic, biochemical and probably better, than a serum test.
immunologic tests on the abdominal fluid are more – Preliminary results indicate that RT-PCR for FCoV
useful than blood tests. These tests include: in the effusion is of high sensitivity and specificity.
● Cytology. Peritoneal fluid from a cat with wet FIP – Adenosine deaminase activity. The level in the
will typically reveal a non-septic exudate. The fluid fluid is usually higher than with other causes, but
is pale to straw-colored, may contain white flecks the test is not routinely available.
(fibrin) and may clot upon standing. Cytology
An FeLV test should be performed.
reveals a high-protein background (stippling, cres-
cent formation) and mature neutrophils. Chylous Exploratory surgery or laparoscopy with reveal multi-
effusion may also occur. focal small (e.g. 1–5 mm) white serosal plaques.
● Total protein, albumin and globulin levels. As in Biopsies of abdominal lesions seen at surgery or
serum, but of more diagnostic value: the higher the laparascopy reveal pyogranulomatous to granuloma-
total protein and globulin level, and lower the albu- tous inflammation. Immunohistochemistry may be
min to globulin ratio, the more likely the cat has FIP. used to demonstrate FCoV antigen within tissues. Viral
Total protein ≥ 120 g/L (12 g/dl) had a specificity of culture may be available through research facilities.
99% and positive predictive value of 89% in one
study, while gamma-globulins ≥ 30 g/L (3.0 g/dl)
Differential diagnosis
and gamma-globulin content >32% in the fluid as
demonstrated by protein electrophoresis have been Differential diagnoses for cats with non-specific signs
reported to have 100% specificity and positive pre- and peritoneal fluid include neoplasia, pancreatitis
dictive values for FIP. An albumin to globulin ratio and right heart failure.