How is FIP Diagnosed in Cats: Understanding the Process and Tools Used

Feline Infectious Peritonitis (FIP) is a serious illness in cats, and figuring out whether a cat has it can be quite tough.

There isn’t a single test that gives a definite “yes” to FIP. Instead, veterinarians have to piece things together by looking at symptoms, lab results, and sometimes using advanced imaging or tissue analysis.

If you’re curious about how vets diagnose FIP, the Cure FIP GCC has put together this simple and informative guide.

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 four types: wet, dry, ocular, and neurological. 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 Test to Help Diagnose FIP in Cats

Noticing symptoms and visible changes is usually step one. But to be more certain, vets will often run additional tests. Here are the four main types that can help identify FIP.

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

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.

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, IHC, and PCR

To confirm FIP, a biopsy can be done. This means taking a small tissue sample from an organ or lymph node and sending it to a lab.

At the lab, a method called IHC (Immunohistochemistry) is used to look for the FIP virus directly in the tissue cells.

But biopsies have some downsides:

• they require anesthesia

• they can be pricey

• results take time to come back
  

Because of this, biopsies aren’t always used unless really necessary. Most vets rely on strong test results combined with symptoms.

Another option is a PCR test. This checks for the genetic material of the FCoV virus in fluids or tissue. If the test detects the mutated strain linked to FIP, it’s more accurate.

Still, it’s not foolproof. Many healthy cats have the regular FCoV virus, so a positive result doesn’t always mean your cat has FIP.

That’s why vets look at these test results together with clinical signs and your cat’s history before making a diagnosis.

Challenges in Diagnosing Dry and Neurological FIP

Among all FIP types, wet FIP is the easiest to detect. This is because pet owners can often notice obvious physical changes, such as a swollen belly.

Additionally, with the Rivalta Test, the fluid buildup in body cavities is generally not hard to identify. Unfortunately, this isn’t the case with dry or neurological FIP.

Dry FIP can affect various organs without any fluid accumulation, which makes the symptoms harder to spot. 

On the other hand, neurological FIP targets the central nervous system and may cause tremors, seizures, loss of balance, or changes in behavior.

Due to the complexity of diagnosing these forms of FIP, a combination of different diagnostic methods is usually needed. 

This can include clinical observation, blood tests, advanced imaging like MRI, and further testing such as PCR or even brain biopsies.

Final Thought

FIP is a complicated illness that can look like several other diseases. That’s why it takes a mix of test results, clinical signs, and your cat’s overall condition to reach a proper diagnosis.

Thankfully, many cats diagnosed with FIP are now being treated with GS-441524. This treatment can stop the virus from spreading and give your cat a real shot at recovery.

If you suspect your cat might have FIP, don’t lose hope. You can contact the Cure FIP GCC Team via WhatsApp for the correct dosage and expert support throughout your cat’s treatment.