GLDH and SDH (liver enzymes) in dogs and cats

What it shows

Both enzymes belong to the “leakage” group: there is much more of them inside liver cells than in the blood, so when cell membranes are damaged, their activity in the blood rises. GLDH lives inside mitochondria and is concentrated around the central veins of the liver lobules — a zone that is hit, for example, when the liver gets too little oxygen. SDH lives in the cell’s cytoplasm; its activity rises within 24 hours of liver injury.

In horses and exotic animals, GLDH does not rise with severe muscle injury. Neither enzyme tells the cause of the injury, and the size of the rise does not show whether the damage will reverse or how well the liver works.

Higher than reference — what it may be a sign of

• Damage to liver cells of any cause — the enzymes do not say which. As a rough guide for leakage enzymes, a 2–3-fold rise above the range is called mild, 4–5-fold moderate and close to 10-fold marked.
• Lack of oxygen in the liver. Because GLDH sits in the zone around the central veins, injury there can raise GLDH more than ALT.
• Ongoing injury. GLDH rises more and can stay raised longer than SDH (data from large animals), so it is the more sensitive of the two for persistent damage.
• The pattern with ALT in dogs. One laboratory interprets a slight GLDH rise with a stronger ALT/AST rise as pointing to an acute process, and the reverse as pointing to a chronic one; it stresses that a single GLDH value has no diagnostic meaning on its own.

A raised value is a sign, not a diagnosis — the vet decides what to look at next.

Lower than reference

Low GLDH or SDH has no clinical meaning. A result below the range, or zero, is simply read as no sign of liver cell leakage — though it does not rule out liver disease, since enzymes show injury, not function.

Look at together with

• ALT — the main liver-injury enzyme for dogs and cats; GLDH is read against it.
• AST and CK — help separate liver from muscle damage.
• ALP and GGT — bile flow and cholestasis rather than cell leakage.
• Bile acids and bilirubin — how well the liver actually works.

Units and conversion

Both enzymes are reported in U/L (international units of activity), so there is nothing to convert. Activity depends on the method and the measuring temperature (usually 37 °C), so results are best compared within one laboratory. In the app each row keeps the unit printed on the form.

Reference range

The reference range is on your lab’s form. In healthy small animals GLDH activity is usually very low, often below about 10 U/L, so a number that looks modest can already be several times above the range. Handling matters: EDTA binds zinc and lowers GLDH and SDH activity, which is why serum or heparin plasma is preferred, although some labs accept EDTA plasma for GLDH. SDH is an unstable enzyme and loses activity in a sample that waits too long; GLDH is more stable in storage.

Cats and dogs

Sources

1. eClinPath (Cornell University College of Veterinary Medicine). GLDH — chemistry / liver / liver injury.
2. eClinPath (Cornell University College of Veterinary Medicine). SDH — chemistry / liver / liver injury.
3. eClinPath (Cornell University College of Veterinary Medicine). Liver injury — chemistry / liver.
4. Whitbread TJ. Clinical Biochemistry. Merck Veterinary Manual, professional version, full review June 2015.
5. LABOKLIN. GLDH — clinical chemistry, enzymes (test description).
6. LABOKLIN. Reference ranges dog, cat, horse — clinical chemistry (12.2022).