Fibrinogen in cats and dogs
Fibrinogen is a liver protein that thrombin turns into fibrin — the mesh that holds a clot together. It is also an acute-phase protein: inflammation makes the liver produce more of it. So a high value usually speaks of inflammation, and a low one of failing production in the liver or of fibrinogen being used up in clotting.
What it shows
Fibrinogen sits at the very end of the clotting chain, so it is both a clotting factor and a marker of inflammation. How it was measured matters:
- Clottable fibrinogen (Clauss method) — the most accurate. It is a modified thrombin time: the plasma is diluted and its clotting time is read off a standard curve, ideally made from the same species. The longer the time, the less working fibrinogen.
- Heat precipitation — a crude estimate from the drop in plasma protein after heating. It moves in steps of 100 mg/dL and cannot detect low values; it is used mainly in horses and ruminants and is not recommended for cats and dogs.
- Fibrinogen antigen — an immunological test in specialised coagulation labs. Compared with the clottable result it shows whether fibrinogen is simply scarce or present but not working (dysfibrinogenemia).
Higher than reference — what it may be a sign of
- Inflammation of any cause. In one study of dogs seen as emergencies, average fibrinogen was about 550 mg/dL with local inflammation and 500 mg/dL with sepsis or systemic inflammation, against about 210 mg/dL in healthy blood donors — but the groups overlapped, so one number does not tell them apart.
- Kidney disease in cats — the reason is not known.
- Some dogs with liver disease — the inflammatory rise can hide the fact that the liver is making less.
- Excitement at the time of sampling can raise fibrinogen and some other clotting proteins.
Lower than reference
- Liver failure — the liver cannot make enough. In dogs values below 100 mg/dL and in cats below 70 mg/dL usually mean failing production or consumption.
- DIC (disseminated intravascular coagulation) — fibrinogen is used up in clotting. Even so, in DIC in dogs it is most often normal or high and low in fewer than 30% of cases, so a value inside the range does not rule DIC out.
- Inherited forms — rare: low or absent fibrinogen, or fibrinogen that does not work.
Very low fibrinogen — below about 75 mg/dL in dogs (50 mg/dL in other species) — lengthens PT and APTT too.
Look at together with
- Thrombin time — reacts to low fibrinogen most sensitively of the clotting times, then APTT, then PT.
- D-dimer — a markedly high D-dimer with low fibrinogen suggests clotting proteins are being consumed.
- Platelets — part of the DIC set together with PT, APTT, fibrinogen and D-dimer.
- CRP, SAA, white blood cells — other signs of inflammation to read it with.
Units and conversion
European labs usually report g/L, North American labs mg/dL. One g/L equals 100 mg/dL, so 2.5 g/L is 250 mg/dL. In the app each row keeps the unit printed on the form; the chart converts to one unit so forms from different labs line up.
Reference range
The reference range is on your lab’s form. It depends on the method and on the standard used. For illustration, one reference coagulation laboratory using the Clauss method with a same-species standard lists 150–490 mg/dL (1.5–4.9 g/L) for dogs and 76–270 mg/dL (0.76–2.7 g/L) for cats. A normal result by heat precipitation does not rule out either inflammation or low fibrinogen.
How the citrate sample is collected is described in the article on PT. Fat (lipemia) and hemolysis do not usually disturb the Clauss method unless the analyser reads clotting optically; they do distort the heat-precipitation estimate.
Cats and dogs
In the laboratory example above the cat interval is lower than the dog one, so dog and cat numbers are not compared. In cats fibrinogen can rise with kidney disease. Values below about 70 mg/dL point to failing production or consumption.
In dogs fibrinogen rises with inflammation of many kinds, but values overlap between local inflammation, sepsis and health. Values below about 100 mg/dL point to liver failure or consumption. Inherited low fibrinogen is reported in Saint Bernards and Vizslas, and fibrinogen that does not work properly in inbred Borzois.
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
- eClinPath (Cornell University College of Veterinary Medicine). Hemostasis — Fibrinogen.
- eClinPath (Cornell University College of Veterinary Medicine). Hemostasis — Coagulation assays.
- eClinPath (Cornell University College of Veterinary Medicine). Hemostasis — Sample collection.
- Center SA. Coagulation Tests in Hepatic Disease in Small Animals. Merck Veterinary Manual, professional version, updated November 2024.
- McQuinn E. Coagulation Protein Disorders in Animals. Merck Veterinary Manual, professional version, updated March 2026.
- Cornell University Animal Health Diagnostic Center, Comparative Coagulation Laboratory. Assay Reference Intervals.
- IDEXX — Coag Dx Citrate PT Test, package insert (sample quality and patient excitement).
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.