GGT in cats and dogs
GGT (gamma-glutamyl transferase) is an enzyme on the surface of cells lining the bile ducts, as well as in the kidney and pancreas. In blood it comes mainly from the liver and rises when bile flow is disturbed or the bile ducts proliferate. It is read alongside ALP: in dogs it is less sensitive but more specific, and in cats it is often the more telling of the two.
What it shows
GGT is bound to cell membranes. The kidney and pancreas contain the most, but they shed it into the urine and the gut rather than into the blood, so blood GGT reflects the liver and above all the biliary tract. When bile ducts are blocked, inflamed or multiplying, and bile acids build up, more GGT is made and released into the blood.
GGT is not a marker of liver cell death: after a single episode of sudden severe liver necrosis it changes little or rises only 1–3 times, settling in about 10 days (Merck). Its strength is bile flow, and in cats it also helps to sort out the causes of a raised ALP.
Higher than reference — what it may be a sign of
- Bile flow problems: a blocked bile duct, inflammation of the bile ducts, liver tumours. With a blocked bile duct GGT climbs over one to two weeks — in dogs to 10–50 times normal, in cats to 4–16 times within two weeks (Merck).
- Medicines: glucocorticoids, phenobarbital, phenytoin and several others can raise GGT (Merck). In dogs the effect of steroids varies; in dogs on phenobarbital the rise in one study was mild, and the average stayed within the range (eClinPath).
- Cushing’s disease in dogs: in one small study GGT was raised in 67% of dogs, sometimes with ALP in range (eClinPath).
- Newborn puppies: colostrum is rich in GGT, and in puppies 2–3 days old activity can reach up to 1000 times the adult level, falling over about 10 days. This is expected and not a sign of disease (eClinPath). Merck notes that this colostrum effect is not seen in kittens.
Lower than reference
A low GGT on its own is not considered a sign of disease. Technical reasons can lower the measured value: marked jaundice (very high bilirubin) and moderate to severe hemolysis in the sample (eClinPath). In cats a low-looking number may simply be typical for the species — feline GGT activity is low, and the feline range is narrower and lower than the canine one.
Look at together with
- ALP — the partner enzyme. In dogs ALP is the more sensitive and GGT the more specific. In cats with inflammatory liver disease or a blocked bile duct GGT may rise more than ALP; in fatty liver it is the other way round (Merck).
- Bilirubin — in feline fatty liver ALP rises first, then bilirubin, and GGT last (eClinPath).
- ALT and AST — show whether liver cells are being injured as well.
- Bile acids and ultrasound — to assess liver function and look at the bile ducts and gallbladder.
Units and conversion
GGT activity is reported in units per litre: U/L, on Russian forms Ед/л or МЕ/л. These are the same unit, so no conversion is needed. Results still depend on the analyzer and the tube: eClinPath notes that an underfilled lithium heparin tube can raise GGT by 10–50%, especially at low activities. Trends are best followed within one lab.
Reference range
The reference range is on your lab’s form. Check that it is the range for the right species: Merck stresses that cats have a narrower and lower GGT range than dogs, so canine limits are not applied to a cat. In a puppy a few days old a very high GGT after suckling is expected. The pairing with ALP and the trend over repeated tests mean more than a single value.
Cats and dogs
In cats GGT is often more informative than ALP: in an older study of cats with liver disease GGT was raised in 83% and ALP in 43% (eClinPath). Merck calls GGT more sensitive but less specific than ALP in feline inflammatory liver disease. Fatty liver (hepatic lipidosis) is the exception: there ALP usually rises much more than GGT, a pattern that helps a vet narrow down the cause.
In dogs GGT is less sensitive than ALP but more specific (Merck). It can rise with steroid medicines and with Cushing’s disease, sometimes even when ALP is still in range, and it falls when the hormonal disorder is controlled. In puppies in the first days of life a very high GGT comes from colostrum and is expected.
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
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.