Confused About FIP Diagnosis? Here’s How It’s Done in Cats

Feline Infectious Peritonitis (FIP) is a serious disease that affects cats. Diagnosing it is often one of the most challenging parts of the journey.

There's no single test that says, "Yes, this is FIP." Instead, vets have to connect the dots using a mix of symptoms, lab results, and sometimes even advanced imaging or tissue tests.

If you're wondering how FIP is diagnosed, here’s a helpful breakdown from Basmi FIP India Team.

Why Diagnosing FIP is So Difficult?

FIP often mimics other illnesses, especially in its early stages. Fever, weight loss, and lack of energy are common. But, these symptoms could also point to many other conditions. 

On top of that, FIP comes in two types: wet (effusive) and dry (non-effusive). Each presents differently, which makes things even more confusing. That’s why multiple tests are usually needed and interpretation must be done carefully.

4 Types of Tests to Help Diagnose FIP in Cats

While observing clinical symptoms and visible signs is the first step, vets usually need more than just that to accurately diagnose Feline Infectious Peritonitis (FIP). 

To be sure, there are four types of test that can help confirm whether your cat might have FIP. Curious about what they are? Let’s break them down one by one!

1. Blood Tests: The First Clue

The first and most common step is a complete blood count (CBC) and blood chemistry test. These help give a general idea of your cat’s health and can show early warning signs that something isn’t right.

Some of the typical signs that raise concern for FIP include:

• Low albumin (a type of protein in the blood),

• High globulin (another blood protein, usually elevated during inflammation),

• Anemia (low red blood cell count, which may cause weakness),

• High white blood cell count (a sign of infection or inflammation), and

• A low A/G ratio (albumin divided by globulin). 
  

If this ratio drops below 0.5, FIP becomes more suspicious. While these results don’t confirm FIP, they act as red flags and help your vet decide if further testing is needed.

2. Specific Tests: Rivalta Test and PCR

If your cat has fluid in the belly or chest—a classic sign of wet FIP—your vet might take a sample of the fluid and run a Rivalta test. 

This simple test helps tell whether the fluid is caused by inflammation like FIP or something else, like heart disease.

• A positive Rivalta result means FIP is more likely.

• A negative result makes FIP less likely, but doesn’t rule it out completely.
  

Another option is the PCR test, which looks for the genetic material of the coronavirus (FCoV) inside the fluid or tissues. This test is more accurate when it finds the mutated form of the virus linked to FIP.

However, it’s not perfect—many healthy cats carry the regular coronavirus, so a positive result doesn’t always mean your cat has FIP.

That’s why these test results must be read together with the cat’s symptoms and medical history.

3. Imaging: X-Rays and Ultrasound

If your cat doesn’t show obvious signs of wet FIP (like a swollen belly from fluid), your vet may suggest imaging tests like X-rays or ultrasounds.

These tools help:

• Detect hidden fluid buildup,

• Spot enlarged organs like the liver, kidneys, or lymph nodes,

• Check for inflammation in the abdomen or chest.
  

Imaging is especially helpful in dry FIP cases, where symptoms are vague or internal.

4. Confirmatory Tests: Biopsy and IHC

The most accurate way to confirm FIP is through a biopsy, where a small sample of tissue (from organs or lymph nodes) is taken and sent to a lab.

There, experts use a special technique called IHC (Immunohistochemistry) to look for the FIP virus directly inside the tissue cells.

However, biopsies:

• Require anesthesia,

• Can be expensive, and

• Take several days to get results
  

Because of these challenges, biopsies are rarely done in everyday cases. Most vets rely on a strong combination of test results and clinical signs instead.

Final Thought

FIP is a complicated disease that can look like many other illnesses. That’s why vets usually combine multiple tests, your cat’s symptoms, and even how your cat responds to treatment to reach a proper diagnosis.

Many cats diagnosed with FIP are now being treated with GS-441524. In simple terms, it stops the disease from spreading and gives your cat a real fighting chance.

So, if your cat is showing signs of FIP, don’t lose hope. You can consult with the Basmi FIP India Team via WhatsApp to get the right dosage and receive expert guidance throughout your cat’s recovery journey.