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FIP Diagnosis in Cats: Tests and Methods for Accurate Diagnosis

!NEWS! "The American Association of Feline Practitioners and EveryCat Health Foundation Announce Feline Infectious Peritonitis (FIP) Diagnosis Guidelines. The guide is comprehensive, and you should show it to your vet if your vet is having a difficulty confirming the diagnosis."
FIP Diagnosis Guide
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Feline Infectious Peritonitis (FIP) is a viral disease that can be fatal to cats. Caused by Feline Coronavirus (FCoV), FIP is prevalent among cats worldwide. However, diagnosing FIP can be challenging because the symptoms can be confused with other illnesses. Here are some ways veterinarians use to diagnose FIP in cats.

Hematology and Serum Chemistry Tests for FIP Diagnosis

Blood tests can provide essential information about FIP. Cats with FIP may have an increase in total serum protein concentration, caused by an increase in globulins. Albumin loss in cats with FIP can also cause the ratio of albumin to globulin to drop, which is a much better way to identify FIP than total serum protein or globulin concentrations.

Other laboratory parameters, like liver enzymes, bilirubin, urea, and creatinine, may also be higher in cats with FIP. Cats with FIP often have hyperbilirubinemia and icterus. High serum levels of -1-acid glycoprotein (AGP), a serum acute-phase protein, can help confirm the diagnosis, but levels are also higher in other inflammatory conditions.

Diagnostic Imaging for FIP Diagnosis

Ultrasound can identify specific findings that should make doctors more suspicious of FIP, like abdominal lymphadenopathy, peritoneal or retroperitoneal effusion, renomegaly, irregular renal contour, hypoechoic subcapsular echogenicity, and diffuse changes in the intestines.

Effusion Fluid Analysis for FIP Diagnosis

Tests on effusion are much better at identifying FIP than tests on blood. The Rivalta's test is a straightforward and cost-effective method that can be performed in a veterinarian's office to differentiate between effusions caused by FIP and those caused by other diseases. It has a high positive predictive value (86%) and a very high negative predictive value (96%).

Measurement of Antibodies for FIP Diagnosis

Antibody testing measures antibodies against FCoV, but there is no test for antibodies specific to FIP. Cats with FCoV antibodies do not always develop FIP, so antibody titers need to be interpreted with caution and should not be the only test used to diagnose FIP. Cats with high antibody titers are more likely to shed FCoV, which is associated with the amount of virus in the intestines and the rate at which the virus replicates.

Rivalta's Test for FIP Diagnosis

Rivalta's test is a straightforward and cost-effective method that doesn't require any specialized laboratory equipment and can be performed in a veterinarian's office. It helps to differentiate between effusions caused by FIP and those caused by other diseases. A positive reaction occurs because of the presence of proteins, fibrin, and inflammatory mediators. The test involves adding a drop of effusion fluid to a tube filled with a solution of distilled water and acetic acid. A positive test is indicated if the drop remains on the surface or slowly sinks to the bottom, while a negative test is when the drop disappears. The Rivalta's test has a high positive predictive value (86%) and a very high negative predictive value (96%).

Cerebrospinal Fluid Analysis for FIP Diagnosis

Cerebrospinal fluid (CSF) analysis from cats with neurological signs due to FIP lesions may reveal an increase in protein and pleocytosis, primarily composed of neutrophils, lymphocytes, and macrophages. However, not all cats with FIP will have abnormal CSF results. In one study, cats with FIP had a CSF protein level of more than 200 mg/dL and a white blood cell count of more than 100 cells/L, most of which were neutrophils.

PCR for FCoV in Feces:

However, FCoV has been found in feces samples using PCR, which is a sensitive and useful way to prove that a cat is shedding FCoV in its feces. The amount of virus in the intestines is linked to how strong the PCR signal is in the poop. These results can help find cats that always shed a lot of viruses and are a big risk in homes with more than one cat.

FCoV Antigen Immunostaining:

The other test commonly used to diagnose FIP is FCoV antigen immunostaining. This test involves staining cells from a fluid or tissue sample with antibodies that detect the presence of the FCoV antigen. The most significant advantage of FCoV antigen immunostaining is its specificity. A positive immunofluorescence staining of intracellular FCoV antigen in macrophages of the effusion was 100% indicative of FIP in a recent study that looked at a large number of cats with confirmed FIP and cats with other confirmed diseases. However, the test cannot tell the difference between the FCoV that doesn't cause FIP and the FCoV that does.


Conclusion: Accurately Diagnosing FIP in Cats

In summary, FIP can be a challenging disease to diagnose due to its similarity to other diseases. Therefore, it is essential to use multiple diagnostic methods, such as hematological and serological tests, diagnostic imaging, and effusion tests, to diagnose FIP in cats. Although FCoV reverse transcriptase PCR can be useful, it should not be relied upon as the only test for diagnosing FIP.

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