FIP Diagnosis

Clinical Symptoms of FIP

If you are reading this page, it may have led you to suspect that your cat has FIP. If so, your cat may have some of the symptoms listed below.

For FIP, cats are predisposed to 2 years of age, but older cats may become ill.
In any case, the manifestations of FIP are in themselves very unspecific, and the diagnosis is usually made when several symptoms are concurrent.


Especially with wet FIP, effusion can occur in the pleural (thoracic) cavity. Measure the cat's respiratory rate. Normal respiratory rate is around 20-30 breaths per minute. If you notice a higher respiratory rate or very shallow breathing (see below), seek the help of a veterinarian immediately !!! It may be necessary to drain a portion of the fluid from the thoracic cavity. Otherwise, the cat is at risk of suffocation or heart failure. Your cat needs first aid.


  • Wet FIP is typical especially for young cats
  • Abdominal distention
  • Sometimes fluid appears in the chest cavity, causing it to make breathing difficult and faster, and the heart is also very stressed.
  • Anorexia
  • Fatigue
  • Apathy
  • Periodic fevers lasting more than 4 days that do not respond to ATB or antipyretics (> 39 ℃)
  • Weight loss
  • Jaundice may appear

The cat breathes hard due to effusion in the pleural cavity

Luna - The world's first privately owned cat treated with GS441524. Photo from the time of diagnosis of wet FIP
Abdomen enlarged with wet FIP.


  • Dry FIP is typical especially for older cats
  • Anorexia
  • Fatigue
  • Apathy
  • Periodic fevers lasting more than 4 days that do not respond to ATB or antipyretics (> 39 ℃)
  • Weight loss
  • Jaundice may appear
  • Pay special attention if the symptoms of the disease have lasted for a long time (more than a month). Dry FIP at a later stage may progress to a wet form, or to even more complicated forms, such as ocular or neurological FIP.

Ocular FIP

The same symptoms as with dry FIP, plus the ones listed below.

  • Ocular lesions (uveitis - inflammation of the uvea, middle layer of the eye ball)
  • Bloody or cloudy eye

Ocular FIP is usually associated with dry FIP, rarely occurring in combination with the wet variant, although this is not completely ruled out.

Cat with ocular form of FIP
Anterior uveitis of a cat with FIP

Neurological FIP

Cat with neurological FIP

The same symptoms apply as for dry FIP and in addition the following may occur:

  • chills,
  • weakness in the hind legs,
  • rigidity,
  • bradykinesia (slow motion),
  • balance disorders,
  • confusion,
  • urinating and performing needs outside the toilet,
  • incontinence,
  • seizures,
  • cramps,
  • paralysis,
  • disorientation,
  • shock conditions.

The spectrum of neurological symptoms is practically unlimited and depends on which areas of the central nervous system are affected.

Dr. Pedersen is of the opinion that the diagnosis of FIP can also be confirmed by starting treatment with GS441524. He recommends it especially in neurological FIP, where most examination methods are very expensive. The cat responds very quickly to the start of treatment with GS. If this happens, it is essentially a confirmation of the diagnosis of FIP.

Examination by a veterinarian

Any of the above symptoms should lead you to a veterinarian, where you should work to confirm or refute the diagnosis of FIP. He should do basic examinations and, if necessary, reach for some specialized ones.

  • basic biochemistry
  • basic hematology
  • FIV / FeLV test
  • medical ultrasound
  • electrophoresis of serum proteins
  • in wet FIP it is good to make a punction and send the fluid for RT-PCR test, or at least visually evaluate its color and consistency…
  • in dry FIP RT-PCR test from a sample of mesenteric lymph node (biopsy)
  • Rivalta test - used to differentiate between exudate and transudate
  • The frequently used SNAP test for antibodies from blood usually has no meaning, as it cannot detect whether it is a mutated FIPV virus or just a common and harmless coronavirus FCoV, which is estimated to have about 70-80% of cats.
  • Serum Amyloid A
  • Alpha-1 acid glycoprotein

The findings for FIP usually correspond to the following findings:

  • The effusion in wet FIP is usually yellow, viscous, sticky, fibrin fibers are formed in it. The presence of liquid will also be shown by sonographic examination. See pictures below.
  • enlarged lymph nodes visible on sonography
  • in dry FIP, local inflammatory foci (granulomas) often occur in some organs, such as the liver or kidneys. They are visible on ultrasound.
  • high coronavirus titer (≥1: 3200)
  • isolated exudates around organs in abdominal cavity

Selected blood parameters important in the diagnosis of FIP

ParameterWet FIPDry FIP
Hematocritreducednormal to decreased
Reticulocytesnormal to decreasednormal to decreased
Lymphocytesdecreasednormal to decreased
Total proteinnormal to elevatednormal to elevated
Albuminnormal to decreasednormal to decreased
Gamma globulinselevatedelevated
A: Gdecreased (<0.5)decreased (<0.5)
Bilirubinelevatednormal to elevated
Acute phase proteins (SAA, AGP)elevatedelevated

Ultrasound image showing abdominal effusion in a cat with wet FIP. Anechoic fluid is present between organs, distending the abdomen. FF = free fluid; L = liver; S = spleen; K = kidney

Efusion fluid in wet FIP

Peritoneal effusion from a cat with classic wet (or effusive) form of FIP.
(A) Characteristic color of peritoneal effusion collected by abdominocentesis.
(B) Close view of a plastic bag containing 350 ml of abdominal effusion and large clumps of fibrin.
Positive Rivalt test in a cat with wet FIP
  • Clear, viscous, yellow, rich in proteins
  • Protein background
  • TP above 35 g/l
  • Few cells (<5x 109/L)
  • Macrophages, non-degenerate neutrophils, fewer lymphocytes
  • AGP in effusion
  • Rivalta's test - positive is not definitive, but negative excludes FIP
  • PCR on effusion
    • High in FIP cats - 72-89 % cases
    • A negative result does not rule out FIP
    • High specificity (amplification is rarely possible even in non-FIP cats)
  • Dg FIP: young patient, suggestive history, clinical examinations and laboratory findings: high protein + few cells in effusion + PCR positive = FIP very likely

Source: Pleural effusion in cats – differential diagnosis and management

Prognosis of FIP survival without treatment

HCT / PCV (%)   > 26
20 - 26
AST  (µkat / L)  <2.5
2.5 - 5
> 5
Total bilirubin (μmol / L)   <9
9 - 38
> 38
Potassium (mmol / L)   4.0 - 5.8
3.0 - 3.9
Sodium  (mmol / L)   156 - 165
150 - 155

Select a score for your parameter values and add them together. The approximate prognosis for treatment-free survival is lower. The table is based on Tsai et al, 2011.

0-4 survival time more than 2 weeks
5-11 survival time less than 2 weeks
> 12 survival time less than 3 days

The final diagnosis itself belongs to the veterinarian. Needless to say, you should have a really good vet.

Selected bloodwork reference values here.