Alpha-1 acid glycoprotein (AGP) in cats and dogs
Alpha-1 acid glycoprotein (AGP) is an acute phase protein: the liver releases more of it when there is inflammation. In cats it is measured mainly when feline infectious peritonitis (FIP) is suspected. A high AGP supports that suspicion, but it also rises with other infections and tumours, so on its own it never confirms or rules out FIP.
What it shows
When tissue is inflamed, signal molecules make the liver change which proteins it releases into the blood. AGP is one of the proteins that go up. In cats and dogs it is a moderate acute phase protein: it is present in healthy animals, rises about 5–10 times after a trigger and peaks around 48–72 hours. On protein electrophoresis it runs in the alpha-1 zone.
AGP is not a test for one disease. Its main practical use is in cats, as one piece of the puzzle when FIP is suspected — together with the history, other blood and fluid findings, and tests that look for the virus in the tissue. AGP can be measured in blood and also in an effusion.
Higher than reference — what it may be a sign of
- FIP in cats — values above about 1500 µg/mL are frequently reported in cats with FIP, in blood and in effusions. In the diagnostic approach of the European Advisory Board on Cat Diseases (ABCD), a serum AGP above about 1500 µg/mL counts as supporting FIP and above about 3000 µg/mL as more strongly supporting it.
- Other infections and tumours — AGP is not specific for FIP. It can also be raised with other infectious diseases and neoplasia; in one study, septic, haemorrhagic and tumour-related effusions also came with high serum AGP.
- Any inflammation — as an acute phase protein, AGP may increase with any inflammatory condition, so a moderate rise has many possible causes.
How much weight a high value carries depends on how likely FIP already looks: a markedly high AGP adds more when the rest of the picture is unclear. The final conclusion belongs to the vet.
Lower than reference
A value within the reference range is the expected result in a healthy animal; low AGP is not linked to any disease of its own. In a cat with suspected FIP, serum AGP below about 1500 µg/mL makes FIP less likely, but it is read together with everything else rather than as a firm “no”.
AGP is also used to follow cats with FIP over time. In a small study, AGP returned to the reference range in every cat that recovered and stayed high in cats that only went into remission; the authors suggest two normal results at least a week apart before calling it recovery.
Look at together with
- Feline coronavirus tests — antibodies and RT-PCR; AGP adds weight to the suspicion, the virus tests and tissue findings decide.
- Serum amyloid A (SAA) — the major acute phase protein of cats; it is also markedly raised in FIP and is more widely available.
- Effusion analysis and Rivalta test — when there is fluid, its protein, cells and AGP are read together.
- Protein electrophoresis and albumin to globulin ratio — other parts of the protein picture in FIP.
Units and conversion
Labs report AGP in µg/mL or mg/L. These are the same quantity: 1 µg/mL equals 1 mg/L, so no conversion is needed. Some guidelines write the thresholds in larger units; the values above are given in µg/mL. Methods differ — radial immunodiffusion, immunoturbidimetric tests and ELISA — and cut-offs may vary between laboratories, so it is best to follow one cat on one method.
Reference range
The reference range is on your lab’s form. One range quoted in the FIP guidelines is below about 480 µg/mL; a commercial feline ELISA used a different, lower range, which shows why the lab’s own range matters. A raised value says that inflammation is present and, in the right cat, supports the suspicion of FIP — it does not say where the inflammation comes from.
Cats and dogs
In cats AGP is a moderate acute phase protein; SAA is the major one. AGP has been studied most in FIP, where high values in serum and effusion are common, and in one study effusion AGP separated FIP from other effusions better than serum AGP. Cats in a household where FIP appeared showed short, moderate rises of AGP shortly before the cases.
In dogs AGP is also a moderate acute phase protein, while CRP and SAA are the major ones, so in practice dogs are tested for AGP less often. Dog-specific assays exist. A raised value in a dog points to inflammation without telling its cause.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Tasker S et al. Feline Infectious Peritonitis: European Advisory Board on Cat Diseases Guidelines. Viruses 2023;15(9):1847
- European Advisory Board on Cat Diseases — FIP: diagnostic approach (tool, September 2023)
- eClinPath (Cornell University College of Veterinary Medicine) — Acute phase proteins
- Merck Veterinary Manual — Feline Infectious Peritonitis
- Measurement of Feline Alpha-1 Acid Glycoprotein in Serum and Effusion Using an ELISA Method: Analytical Validation and Diagnostic Role for Feline Infectious Peritonitis. Pathogens 2024;13(4):289
- Alpha-1 acid glycoprotein reduction differentiated recovery from remission in a small cohort of cats with feline infectious peritonitis. Viruses 2022;14(4):744
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.