FIP Diagnosis: 5 Tests Your Vet Should Run Before Starting Treatment
- DVM Vien
- 5 days ago
- 3 min read
Quick answer: FIP cannot be confirmed by any single test. Diagnosis is a pattern across five: (1) full blood panel showing low A:G ratio and high globulins, (2) fluid analysis if wet FIP is suspected (Rivalta test + cytology), (3) AGP (alpha-1 acid glycoprotein) measurement, (4) ultrasound or X-ray for free fluid or organ lesions, (5) PCR on fluid or tissue if available. Together, these confirm the diagnosis. Treatment should not start without bloodwork showing the characteristic pattern.
Why FIP is hard to diagnose
FIP mimics many other feline diseases — lymphoma, hepatic lipidosis, toxoplasmosis, congestive heart failure, and chronic kidney disease can all produce similar symptoms. There is no single FIP test with 100% specificity. The right approach is pattern recognition across several markers, weighed against the clinical picture and stage-by-stage symptoms.
Test 1: Full blood panel (CBC + biochemistry)
The cornerstone of FIP diagnosis. Look for the classic pattern: low A:G ratio (under 0.4), high serum globulins (often above 55 g/L), low albumin (low 20s g/L), lymphopenia (lymphocytes under 1.5 × 10⁹/L), and frequently mild anemia. Each marker alone is non-specific; the combination is strongly suggestive of FIP. See our full bloodwork guide for what each marker means.
Test 2: Fluid analysis (for suspected wet FIP)
If the cat has a visibly distended abdomen or breathing difficulty, your vet should aspirate a small fluid sample for analysis. FIP fluid is highly characteristic: pale yellow, viscous, high in protein (over 35 g/L), low in cellularity, positive Rivalta test. Cytology shows mostly macrophages and neutrophils. This single test has high specificity for wet FIP — when it matches, treatment can begin without further confirmation. See wet vs dry FIP comparison for the forms.
Test 3: AGP (alpha-1 acid glycoprotein)
AGP is an acute-phase protein that rises sharply in inflammation. Normal feline AGP is under 0.5 g/L; active FIP often shows AGP above 1.5 g/L, sometimes 3–5 g/L. Useful especially for dry FIP where bloodwork can be subtler. Not all EU labs run AGP routinely — you may need to request it explicitly.
Test 4: Imaging (ultrasound or X-ray)
Abdominal ultrasound looks for free abdominal fluid, enlarged lymph nodes, and organ-specific lesions. Chest X-ray (or ultrasound) checks for pleural effusion if breathing is laboured. For neurological signs, MRI is the gold standard but rarely needed — clinical signs plus bloodwork usually suffice for neurological FIP suspicion.
Test 5: PCR on fluid or tissue
PCR detects feline coronavirus RNA in effusion fluid, tissue biopsy, or sometimes blood. A positive PCR plus clinical signs plus bloodwork pattern is essentially definitive for FIP. PCR alone is not enough — many healthy cats carry FCoV without FIP. The combination is what matters. See FCoV vs FIP guide for the distinction.
Decision tree: when to start treatment
Clinical signs + classic bloodwork pattern + positive fluid analysis (wet FIP): start treatment now
Clinical signs + bloodwork pattern + elevated AGP (dry FIP): start treatment now
Clinical signs + ambiguous bloodwork: add AGP and PCR before committing
Clinical signs only, no bloodwork pattern: keep investigating, FIP may not be the right diagnosis
Time matters — earlier treatment improves survival — but starting treatment on the wrong diagnosis wastes 84 days and money. Get the diagnostic pattern right first, then move fast.
Frequently Asked Questions
Can FIP be confirmed without PCR?
Yes — in most clinical practice, FIP is diagnosed on the combination of clinical signs, bloodwork pattern, AGP, and (for wet FIP) fluid analysis. PCR is a useful confirmation but not always needed.
What if my vet isn't sure FIP is correct?
Push for the full diagnostic panel above. Many general-practice vets have limited recent experience with FIP because it was historically untreatable. Free consultation with our team can help interpret results.
How much does the full diagnostic workup cost?
Roughly €150–300 across all 5 tests, depending on country. PCR adds €60–120 if used. See our treatment cost breakdown for the full picture.
Informational only — not veterinary advice. Diagnostic decisions belong to your treating vet.
Comments