ALB/GLOB Ratio in Cats: What It Means — FIP, IBD, and Liver Disease
Last reviewed: April 2026
The albumin:globulin (A:G) ratio is the single most diagnostically powerful calculation in feline bloodwork. Normal range is approximately 0.8–2.0. An A:G ratio below 0.4 in a cat with any fluid accumulation — ascites, pleural effusion, or pericardial fluid — is highly suspicious for FIP (feline infectious peritonitis) and should trigger FIP-specific testing before pursuing any other workup. A normal or near-normal A:G ratio with low albumin points in the opposite direction: gut protein loss from IBD or GI lymphoma, where both albumin and globulin fall proportionally.
Normal ALB/GLOB ratio (cat): 0.8–2.0. A:G below 0.4 + effusion = FIP workup immediately. Normal A:G with low albumin = IBD, liver, or kidney loss.
Abnormal A:G ratio on your cat's panel?
Upload bloodwork to see the A:G ratio together with albumin, globulin, total protein, and other values — the pattern immediately flags FIP, IBD, liver disease, and kidney protein loss.
Analyze My Cat's Protein ValuesWhy the A:G Ratio Matters More in Cats Than Dogs
In dogs, the A:G ratio is useful for directing further testing but doesn't strongly point to any single disease. In cats, FIP creates a distinctive biochemical signature — very high globulins with simultaneously low albumin — that produces ratios below 0.4 and is specific enough to change clinical decision-making before any invasive testing.
FIP is the single most important reason to calculate the A:G ratio in a sick cat, and it's the reason the ratio gets mentioned in almost every feline bloodwork interpretation guide. No other common feline disease creates the same inverted pattern.
The Three Diagnostic Patterns
Pattern A — Low A:G (<0.4): FIP Pattern
FIP drives globulins markedly high while albumin drops. With effusion, this pattern is highly specific for FIP. Start Rivalta test, FCoV PCR, antibody titers.
Pattern B — Normal A:G with Low Albumin: PLE Pattern
IBD and GI lymphoma leak both fractions proportionally — pan-hypoproteinemia. A:G stays normal because both fall together. Also: low cholesterol, low B12. GI workup next.
Pattern C — Mildly Low A:G with Low Albumin: Liver / PLN Pattern
Liver failure or PLN: albumin is selectively depleted while globulins are maintained. Check liver enzymes, bile acids, and urine UPC ratio to differentiate.
A:G Ratio Reference Chart
FIP highly likely if effusion is present. Start FIP workup immediately — Rivalta test, FCoV PCR, antibody titers.
Albumin is low relative to globulin. Check whether globulin is elevated (early FIP, chronic infection) or albumin is selectively low (liver, PLN).
Normal balance. Check absolute albumin and globulin — PLE can show normal ratio with both fractions low. FIP less likely but not excluded.
| Ratio | Likely Meaning | Next Step |
|---|---|---|
| <0.4 | FIP highly likely if effusion present. Very high globulins + low albumin. | Rivalta test, FCoV PCR, antibody titers immediately |
| 0.4–0.8 | Albumin low relative to globulin. Could be early FIP, liver disease, or PLN. | Check absolute values; liver panel; urine UPC; ultrasound for effusion |
| 0.8–2.0 | Normal balance. FIP less likely. PLE possible if both fractions are low. | Check absolute albumin and globulin; GI workup if both fractions low |
FIP: Why the A:G Ratio Gets Inverted
FIP is caused by a mutant form of feline coronavirus (FCoV) that infects macrophages and triggers uncontrolled systemic inflammation. Two simultaneous processes drive the A:G ratio below 0.4:
- • Globulins surge: The liver produces massive quantities of acute-phase proteins (fibrinogen, haptoglobin, alpha-2-macroglobulin), and the immune system produces immunoglobulins against the viral antigens. Globulin commonly rises to 5–8+ g/dL in FIP.
- • Albumin falls: Albumin is consumed by the inflammatory process, lost into effusion fluid, and the liver's albumin production is outpaced by demand. Values of 1.5–2.0 g/dL or lower are common.
The result: if albumin = 1.6 g/dL and globulin = 6.0 g/dL, A:G = 0.27. This value, combined with ascites or pleural fluid, gives a pre-test probability for FIP that is high enough to justify FIP-specific testing before pursuing endoscopy, biopsy, or other expensive diagnostics.
IBD and GI Lymphoma: Why the A:G Ratio Stays Normal
IBD and small cell GI lymphoma cause protein-losing enteropathy (PLE) — the damaged gut wall leaks both albumin and globulin non-selectively into the gut lumen. Because both fractions fall proportionally, the A:G ratio stays in the normal range even as total protein plummets.
This is the key difference from FIP. A cat with albumin of 1.6 and globulin of 1.8 has an A:G ratio of 0.89 — normal — but has severe pan-hypoproteinemia from PLE. A:G ratio alone would not flag this; you need to check the absolute values. Low cholesterol and low B12 (cobalamin) are the supporting clues that confirm gut protein loss.
Important Caveats
- • A normal A:G does not rule out FIP — early or dry-form FIP may not yet show an inverted ratio. Use A:G as a screening tool, not an exclusion rule.
- • A:G below 0.4 without effusion is still suspicious but less specific — investigate further before concluding FIP.
- • Dehydration raises both albumin and globulin — rehydration before repeat testing may reveal a lower ratio than the dehydrated sample showed.
- • Globulin is a calculated value (TP minus albumin) — measurement errors in either total protein or albumin propagate into the ratio.
What Happens Next?
- • If A:G <0.4 + any effusion: Rivalta test on effusion fluid, FCoV PCR, FCoV antibody titers — FIP workup before other invasive testing
- • If A:G normal + low albumin + low globulin: GI workup — ultrasound (intestinal wall thickening, lymphadenopathy), endoscopy, and biopsy for IBD vs. GI lymphoma
- • If A:G low + albumin low + globulin normal: Liver panel (ALT, ALP, GGT, bile acids) and urine UPC to differentiate liver failure from PLN
- • If A:G low + globulin very high + albumin normal: Check for chronic infections, lymphoma; consider SPEP
- • Serum protein electrophoresis (SPEP): If myeloma suspected or globulin >6 g/dL
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Related Reading
Low Albumin in Cats
Why albumin drops in cats — FIP, IBD, GI lymphoma, liver disease — and how to interpret the A:G ratio.
Globulin in Cats
What high and low globulins mean — the FIP pattern, PLE pattern, and chronic infections.
Total Protein in Cats
What high and low total protein means — FIP, IBD, dehydration, and the A:G ratio in context.
FIP in Cats
How FIP creates the inverted A:G ratio — globulins surge, albumin drops.
IBD in Cats
IBD causes pan-hypoproteinemia with a normal A:G ratio — the opposite of FIP.
Frequently Asked Questions
What is the ALB/GLOB ratio in cats?
The ALB/GLOB ratio (A:G ratio) is albumin ÷ globulin. Normal range is approximately 0.8–2.0. In cats, this ratio has exceptional diagnostic importance: A:G below 0.4 with fluid accumulation is highly suspicious for FIP and should trigger immediate FIP-specific testing.
What does a low ALB/GLOB ratio mean in cats?
A low ratio (below 0.8) means albumin is low relative to globulin. The most important cause is FIP: globulin surges while albumin drops, creating ratios below 0.4. Other causes include liver failure and PLN — but these typically don't drop the ratio as severely as FIP.
What does an ALB/GLOB ratio below 0.4 mean in cats?
An A:G ratio below 0.4 — especially with ascites, pleural effusion, or pericardial fluid — is highly suspicious for FIP. FIP drives globulins very high (massive acute-phase protein production) while albumin simultaneously falls. This is one of the most specific non-invasive FIP clues on routine bloodwork.
Does a normal A:G ratio rule out FIP in cats?
No. Early FIP or dry-form FIP may not yet show an inverted ratio. The A:G ratio is a screening clue, not a standalone diagnostic test. FIP diagnosis requires fluid analysis (Rivalta test), FCoV PCR, antibody titers, and sometimes biopsy. A normal ratio reduces suspicion but does not exclude FIP.
What causes a normal or high A:G ratio with low albumin in cats?
When albumin is low but the A:G ratio stays normal, globulin is also low (or fell proportionally). This points to PLE (IBD, GI lymphoma — both fractions lost together), PLN (albumin selectively lost, globulins preserved), or liver disease. This pattern is essentially the opposite of FIP.
What is the A:G ratio in FIP vs IBD in cats?
FIP: A:G ratio typically below 0.4 — globulin very high, albumin low. IBD/GI lymphoma (PLE): A:G ratio typically normal — both albumin and globulin fall proportionally. This distinction is the key bloodwork differentiator between these two conditions before more invasive testing.