In cats with FIP who have ascites, sampling the fluid accumulation (ascites) is the most useful diagnostic step in diagnosing effusionous FIP.
In the absence of effusion, diagnosing FIP is challenging because of the large number of possible clinical symptoms and most of them are nonspecific (eg, anorexia, lethargy, weight loss, fever, all of which were mentioned in the previous section).
Routine blood and biochemical tests
In cats with FIP, there are many common laboratory findings, none of which are characteristic.
In general, lymphopenia and neutropenia in blood routine are typical features of FIP, but they can also occur in many other diseases.
Cat friends who have taken cats to the hospital for biochemical examination should know the biochemical report of cats. There are three of them, globulin (GLOB), albumin (ALB) and total protein (TP). Then the total protein (TP) here is the sum of albumin + globulin, and the so-called white globulin ratio is the ratio of albumin to globulin.
The most consistent laboratory finding in FIP was an increase in the total protein index on the biochemical report, which can reach concentrations ≥12 g/dL. This is found in approximately 50% of cats with wet and 70% of cats with dry IP. The increase in total protein was mainly caused by the increase in globulin.
However, the ratio of albumin to globulin is of higher diagnostic value.
If the ratio of albumin to globulin > 0.8, FIP is almost ruled out
If 0.5<albumin to globulin ratio<0.8, the cat has a higher probability of having FIP
If the albumin to globulin ratio is < 0.5, the cat has a very high probability of having FIP
Other laboratory parameters, including liver enzymes, bilirubin, urea (or BUN), and creatinine, may increase depending on the extent and location of organ damage but are not helpful in establishing an etiological diagnosis.
Serum amyloid A (SAA), another acute-phase protein, was increased 10-fold in serum in cats with FIP compared to asymptomatic cats exposed to feline enteric coronavirus.
Routine imaging: Ultrasound and radiology findings
Ultrasonography or x-rays can be used to identify or confirm the presence of fluid accumulation and to assist in taking a sample. A review of abdominal ultrasonographic findings in 16 cats with FIP revealed peritoneal effusion in 7, retroperitoneal effusion in 1, and abdominal lymphadenopathy in 9. The livers of 11 cats were normal and the remaining cats had anechoic or hypoechoic livers.
Fluid (Ascites) Test (Li Fanta Test)
Fluid testing has a higher diagnostic value than blood testing. The protein content of FIP effusions is very high, with a total protein concentration usually >3.5 g/dL.
The Rivalta (Li Fanta) test is a simple, inexpensive point-of-care test that requires no special laboratory equipment and can be easily performed in a veterinary hospital. It is useful for differentiating fluid accumulations caused by FIP from those caused by other diseases.
A clear reagent tube (10 mL) was filled with approximately 8 mL of distilled water, to which was added 1 drop of acetic acid (high strength vinegar, 98%) and mixed well. On the surface of this solution, carefully instill 1 drop of effusion.
If the droplet disappears and the solution remains clear, the Livata test is defined as negative. The test was defined as positive if the droplet retained its shape, remained attached to the surface, or slowly floated to the bottom of the tube (droplet or jellyfish).