FIP Bloodwork Explained: What to Track Through the 84-Day Protocol
- DVM Vien
- May 12
- 4 min read
Quick answer: The 5 most important FIP bloodwork markers are: A:G ratio (albumin to globulin), serum globulin, serum albumin, AGP (alpha-1 acid glycoprotein), and lymphocyte count. Run a complete panel at day 0 (baseline), day 28, day 56, and day 84 of treatment. A:G ratio below 0.4 with elevated globulins and lymphopenia strongly suggests FIP. By day 28 of GS-441524 treatment, A:G should be trending up and globulin trending down. By day 84, most markers should be within normal range. Continued abnormal values at day 84 suggest residual disease.
Why bloodwork matters more than how your cat looks
Visible clinical signs (fluid resolution, weight gain, energy returning) are reassuring but lag behind what's happening inside the body. Bloodwork captures the underlying inflammation, immune response, and protein imbalance that define FIP. A cat that looks well at day 60 but still shows abnormal globulin and A:G ratio is not yet in remission, even if owners want to declare victory.
Bloodwork is also the tie-breaker during the 84-day observation period when ambiguous symptoms might or might not signal relapse.
The 5 critical markers for FIP
1. A:G ratio (albumin-to-globulin)
The single most useful FIP screening marker. Calculated by dividing albumin by globulin. Normal feline range is 0.6–1.2. An A:G below 0.4 has high specificity for FIP (especially the dry form). Above 0.8 makes FIP very unlikely. During treatment, A:G should rise steadily, week by week, returning into normal range by day 56–84.
2. Serum globulin
Normal range is roughly 28–51 g/L in cats. Active FIP usually pushes globulin above 55 g/L, often into the 70–90 g/L range. The elevation reflects the immune system's antibody response to coronavirus. Globulin should fall steadily during treatment, ideally by 5–10 g/L per month, returning toward normal by day 84.
3. Serum albumin
Normal range is 28–39 g/L. Active FIP pulls albumin down (typically into the low 20s) because the inflammatory state and fluid losses deplete it. Rising albumin during treatment is one of the clearest signs that the cat's protein balance is recovering. Expect 2–4 g/L rises per month during successful treatment.
4. AGP (alpha-1 acid glycoprotein)
AGP is an acute-phase protein — it rises sharply in any inflammatory state, including FIP. Normal feline AGP is under 0.5 g/L. Active FIP typically shows AGP above 1.5 g/L, often into the 3–5 g/L range. AGP is less specific than A:G ratio but more sensitive — it detects inflammation that hasn't yet shown up in other markers. Note that not all vet labs run AGP routinely; you may need to request it.
5. Lymphocyte count
Normal feline lymphocytes: 1.5–7.0 × 10^9/L. Active FIP commonly shows lymphopenia — lymphocytes dropping below 1.5, often around 0.8–1.2. Returning lymphocyte counts during treatment indicate immune recovery. Persistent lymphopenia at day 84 suggests treatment hasn't fully cleared the virus.
Recommended bloodwork schedule
Day 0 (before starting treatment): full CBC, biochemistry, AGP — baseline
Day 28: repeat panel — confirm treatment is working
Day 56: repeat panel — check trend continues
Day 84: final panel — confirm safe to enter observation period
Day 84 post-treatment (final observation): one more panel to confirm sustained remission
Each bloodwork panel costs roughly €60–120 in most EU countries. Total monitoring cost across the 168-day protocol: €240–480. See our treatment cost breakdown for the full budget.
What good trends look like (worked example)
A 4 kg adult cat with wet FIP, treated successfully on the 84-day protocol, typically shows these trends:
A:G ratio: 0.3 (day 0) → 0.45 (day 28) → 0.65 (day 56) → 0.85+ (day 84)
Globulin: 75 g/L → 62 → 52 → 45 g/L
Albumin: 23 g/L → 26 → 30 → 33 g/L
AGP: 3.2 → 1.8 → 1.0 → 0.5 g/L
Lymphocytes: 1.0 → 1.6 → 2.3 → 3.0 × 10^9/L
Steady improvement across all 5 markers, with most values approaching or entering normal range by day 84.
Warning signs in bloodwork trends
A:G ratio stuck or falling — suggests inadequate dose or treatment failure
Globulin not falling by day 28 — contact our team, dose adjustment may be needed
AGP plateauing high — suggests ongoing inflammation, possibly in CNS
Liver enzymes (ALT, AST) rising significantly — may need a brief dose reduction; consult vet
New abnormalities appearing after improvement — possible relapse, even if symptom-free
Share your bloodwork results with us at any of the testing intervals — we'll review the trend and flag anything that needs attention. See more on how supplier quality and dose adherence affect outcomes in our survival rate analysis.
Frequently Asked Questions
Can a single bloodwork panel diagnose FIP?
No. Bloodwork supports diagnosis but doesn't confirm it on its own. Diagnosis combines clinical signs, bloodwork patterns, imaging, fluid analysis (for wet FIP), and sometimes PCR testing. A:G ratio under 0.4 with elevated globulin is highly suggestive but not 100% specific.
What if my vet doesn't run AGP?
Many EU labs offer AGP if you request it explicitly. If your local vet's lab doesn't, you can use the other 4 markers (A:G, globulin, albumin, lymphocytes) to track progress reliably. AGP adds sensitivity but isn't strictly required.
How long does it take for markers to normalise?
Most cats see A:G ratio enter normal range by day 56–84. Globulin and lymphocyte counts often take longer — sometimes into the 84-day observation period. As long as the trend is positive, slight residual abnormality at day 84 isn't alarming.
What if bloodwork looks worse at day 28?
Contact us immediately. Likely causes: dose too low (recalculate using current weight), product purity issue, missed doses, or a need to switch FIP form classification (wet to dry escalation). We'll review and recommend a course of action with your consulting vet.
Informational only — not veterinary advice. Always have a licensed vet interpret bloodwork.
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