How Is FIP Diagnosed? A Step by Step GCC Owner Guide

Key takeaway: There is no single test that confirms Feline Infectious Peritonitis (FIP) on its own. FIP is diagnosed by combining your cat's age and history, clinical signs, blood work (especially the albumin to globulin, or A:G, ratio), fluid analysis if effusion is present, and PCR testing, which your veterinarian reads together as one picture. In the GCC, the challenge is often finding a clinic that runs the full panel, so knowing what to ask for matters.

FIP is caused by a mutation of feline coronavirus, and it moves quickly once signs appear. Getting a clear, structured diagnosis is the first step toward starting an evidence based antiviral plan under veterinary supervision. Below is exactly how the process works and what you should request at each stage.

A cat resting comfortably at home.

How is FIP diagnosed in cats?

FIP is diagnosed through a combination of clinical signs, blood work, fluid analysis, and PCR testing, not by one standalone test. Your veterinarian builds a case from several results, because feline coronavirus is common and only a small fraction of infected cats develop FIP.

The typical patient is a young cat, often under two years old, frequently from a multi cat home or shelter background. Common signs include a persistent fever that does not respond to antibiotics, weight loss, poor appetite, and lethargy. If your vet has raised the possibility, our guide on what to do if your vet suspects FIP walks you through the calm, methodical next steps.

What blood tests point to FIP?

The blood tests that most strongly point to FIP are a complete blood count (CBC) and a biochemistry panel showing high total protein, high globulins, low albumin, and often mild anaemia. These patterns are supportive of FIP but are not conclusive on their own.

On a CBC, vets frequently see a low lymphocyte count and non regenerative anaemia. On biochemistry, elevated globulins driven by inflammation are one of the most consistent findings.

Bilirubin may also be raised, which can show up as yellowing of the gums, eyes, or skin. If your cat looks jaundiced, our guide to jaundice in cats explains why this happens and what it can indicate.

What is the A:G ratio and why does it matter?

The A:G ratio compares albumin to globulin in the blood, and a low ratio is one of the most useful early flags for FIP. Evidence shows that a ratio below roughly 0.4 raises suspicion, while a ratio above 0.8 makes FIP much less likely.

The reason is simple. FIP drives up globulins (the inflammatory proteins) while albumin often drops, so the ratio falls. It is a screening signal, not a verdict.

A borderline ratio does not confirm or rule out FIP. Your veterinarian will read it alongside the clinical picture and further testing before drawing any conclusion.

What does the FIP PCR test show?

A PCR test (often RT-PCR) detects feline coronavirus genetic material in blood, effusion fluid, or affected tissue, and a positive result on the right sample strongly supports an FIP diagnosis. It is most reliable when run on effusion fluid or a tissue aspirate rather than blood alone.

A positive PCR confirms the virus is present, but because feline coronavirus is widespread, context still matters. A negative PCR does not fully exclude FIP either, since the virus is not always detectable in every sample.

This is why the FIP PCR test is used to strengthen a diagnosis rather than to stand alone. Ask your GCC clinic whether they can send samples to a lab that runs feline coronavirus RT-PCR if they cannot do it in house.

What is a Rivalta test and effusion analysis?

If your cat has fluid in the abdomen or chest, analysing that fluid is one of the most valuable diagnostic steps. FIP effusion is typically straw yellow, thick, and high in protein, and the Rivalta test is a simple, low cost bedside check that supports the diagnosis.

In the Rivalta test, a drop of the effusion is added to a solution. If the drop holds its shape and sinks slowly, the result is consistent with FIP.

Lab analysis of the fluid adds cell counts and protein levels, and PCR can be run on the same sample. For cats with effusion, this fluid work is often the fastest route to clarity.

What are the four forms of FIP and how do symptoms differ?

FIP takes four forms: wet, dry, ocular, and neurological. Each shapes both the signs your vet looks for and the antiviral dosing plan that follows, which is why diagnosis and treatment stay aligned around these four categories.

Wet (effusive) FIP

Wet FIP is defined by fluid buildup in the abdomen or chest, causing a swollen belly or laboured breathing. This is the form where effusion analysis and the Rivalta test are most useful, because there is fluid to sample.

Dry (non-effusive) FIP

Dry FIP produces little or no fluid and instead causes inflammatory lesions in organs. It is harder to diagnose, relying more heavily on blood work, imaging, and PCR, and it often presents with vague signs like fever and weight loss.

Ocular FIP

Ocular FIP shows up in the eyes, with signs such as colour changes to the iris, cloudiness, or inflammation inside the eye. An eye exam by your veterinarian is central here, alongside the standard blood work.

Neurological FIP

Neurological FIP affects the brain and spinal cord, causing signs like wobbliness, seizures, tremors, or behaviour changes. Diagnosis may involve neurological examination and, where available, advanced imaging, and this form requires higher antiviral dosing.

Step by step: how FIP diagnosis usually proceeds in a GCC clinic

The diagnostic process is best followed as a clear sequence, because each step narrows the possibilities. Here is the order it typically takes:

1. History and physical exam. Your vet reviews your cat's age, living situation, and signs, then examines for fever, jaundice, fluid, or eye changes.

2. Blood work. A CBC and biochemistry panel check globulins, albumin, the A:G ratio, bilirubin, and anaemia.

3. Fluid analysis, if effusion is present. The Rivalta test plus lab cell counts and protein levels on any abdominal or chest fluid.

4. Imaging. Ultrasound or X-ray to detect fluid, enlarged lymph nodes, or organ changes.

5. PCR testing. Feline coronavirus RT-PCR on effusion, tissue, or blood to confirm viral presence.

6. Diagnosis and staging. Your vet combines all results and identifies which of the four forms is present so a treatment plan can be built.

What tests should you ask your GCC vet for?

Because not every Gulf clinic runs the full FIP panel, it helps to arrive knowing what to request. Ask specifically about:

• A CBC and full biochemistry panel, including total protein, globulins, albumin, and the A:G ratio

• Bilirubin levels if your cat looks jaundiced

• The Rivalta test and lab fluid analysis if there is any effusion

• Feline coronavirus RT-PCR, and whether samples can be sent to an external lab if needed

• Abdominal ultrasound or chest imaging where appropriate

If you would like help reading the numbers once results are in, our article on FIP blood test results explained breaks down what each value means.

What happens after an FIP diagnosis?

Once FIP is confirmed, treatment centres on GS-441524, the antiviral at the core of modern FIP care. A standard course runs 84 days (12 weeks) under veterinary supervision, with dosing set by the form of FIP your cat has.

GS-441524 monotherapy has a 92% success rate reported by UC Davis (Pedersen, 2019), and it remains the proven hero of FIP treatment. More than 100,000 cats have been treated across the CureFIP network since 2019.

The injectable dosing from our catalog is matched to the four forms, which mirrors the diagnostic categories above:

FIP form	GS-441524 injectable dose	Schedule	Duration
Wet	6 mg/kg	1 subcutaneous injection per day, 7 days/week	84 days
Dry	8 mg/kg	1 subcutaneous injection per day, 7 days/week	84 days
Ocular	10 mg/kg	1 subcutaneous injection per day, 7 days/week	84 days
Neurological	10 mg/kg	1 subcutaneous injection per day, 7 days/week	84 days

GS-441524 Antiviral Injectables are available in 20 mg/ml at AED359.00, 30 mg/ml 10ML at AED479.00, and 40 mg/ml at AED599.00. Your veterinarian will confirm the concentration and volume that suit your cat's weight and form of FIP.

There is also an oral route. CURE FIP™ Dual Antiviral Oral Capsules (GS-441524 + EIDD-1931) are priced at AED499.00 and dosed by weight band, positioned for wet and dry cases, with a reported 78.3% remission in the dual antiviral study by Li and Cheah (2025). Some regions note the dual oral capsules are not recommended once ocular or neurological signs are present or if a cat cannot eat or defecate, so this is a decision to make with your vet. You can read more in our overview of why two antivirals can be better than one.

For a full picture of the road ahead, our GS-441524 treatment timeline guide explains what each stage of the 84-day protocol looks like.

FAQ

Is there a single test that confirms FIP?

No. FIP is diagnosed by combining clinical signs, blood work such as the A:G ratio, fluid analysis, and PCR testing, which your veterinarian reads together rather than relying on any one result.

What A:G ratio suggests FIP?

An A:G ratio below roughly 0.4 raises suspicion of FIP, while a value above 0.8 makes it much less likely. It is a screening signal that must be read alongside other findings, not a standalone diagnosis.

Can dry FIP be diagnosed without effusion?

Yes. Dry FIP produces little or no fluid, so diagnosis leans more on blood work, imaging, PCR, and clinical signs. It can take longer to confirm than wet FIP because there is often no fluid to sample.

Does a positive coronavirus PCR mean my cat has FIP?

Not on its own. Feline coronavirus is common, so a positive PCR supports the diagnosis but must be interpreted with clinical signs and blood work by your veterinarian.

How soon should treatment start after diagnosis?

FIP progresses quickly, so most veterinarians recommend starting the GS-441524 based 84-day protocol promptly once the diagnosis is made. Speak with your vet about timing for your cat's specific form.

If your cat has just been diagnosed, or you are still gathering test results, we are here to help you understand the options and plan the next step calmly. Explore the available treatments and speak with our team or your own veterinarian through the CureFIP GCC team, and let your veterinarian guide every medical decision along the way.