CK-MB in cats and dogs

What it shows

Creatine kinase (CK) sits inside muscle and brain cells. It exists in three main isoenzymes: CK-BB (CK-1), found mostly in the brain; CK-MB (CK-2), with its highest concentration in heart muscle and lesser amounts in skeletal muscle; and CK-MM (CK-3), the skeletal-muscle form, which accounts for most of the CK in the blood of animals. There is also a mitochondrial form, about 15% of total CK activity in the heart, and “macro-CK” — CK bound to antibodies.

Because the heart is small compared with the mass of skeletal muscle, total CK rarely rises after heart injury in animals. CK-MB may show a rise, but only when the isoenzymes are separated by electrophoresis, and isoenzymes are hard to identify in animals — some veterinary teaching laboratories do not quantify them at all. CK also leaves the blood quickly, within hours. For these reasons, troponin is used as the marker of heart muscle injury in animals.

Higher than reference — what it may be a sign of

• Damage to the heart muscle — possible, but in animals a rise is reliably seen only with electrophoretic separation; a vet will rely on troponin to judge the heart.
• Skeletal muscle damage — CK-MB is also present in skeletal muscle, so a raised value does not by itself prove that the heart is the source. Total CK rises markedly in muscle breakdown and in aortic thromboembolism.
• Haemolysis in the sample — substances from red blood cells take part in the reaction and can falsely raise measured CK activity.

Lower than reference

A low or undetectable CK-MB has no known clinical meaning. In the blood of animals most CK is the skeletal-muscle form, so a small CK-MB share is expected.

Look at together with

• Troponin — the marker of heart muscle injury in animals.
• Total CK — CK-MB is always read next to it; a high total CK points first to skeletal muscle.
• NT-proBNP — another heart marker, read together with troponin.
• AST and LDH — also present in heart muscle but not specific to it; AST comes from liver and skeletal muscle as well, and LDH isoenzymes are not separated in routine practice.

Units and conversion

CK-MB is reported as enzyme activity in U/L — units per litre. No conversion is needed. Activity depends on the method, so values from different laboratories are compared with care, and a trend is followed in one laboratory. In the app the row keeps the number and unit printed on the form.

Reference range

The reference range is on your lab’s form. Some veterinary laboratories do not measure CK isoenzymes in animals at all. If the test was run on an analyser designed for human samples, it is worth asking the laboratory whether the interval was set for the species of your pet. A value inside or outside the range is read together with total CK and troponin, not on its own.

Cats and dogs

Sources

1. eClinPath (Cornell University College of Veterinary Medicine) — Creatine kinase.
2. Gavazza A, Fruganti A, Turinelli V, et al. Canine Traditional Laboratory Tests and Cardiac Biomarkers. Frontiers in Veterinary Science, 2020;7:320.
3. Gavazza A, Marchegiani A, Guerriero L, et al. Updates on Laboratory Evaluation of Feline Cardiac Diseases. Veterinary Sciences, 2021;8(3):41.
4. Whitbread TJ. Clinical Biochemistry. Merck Veterinary Manual, professional version, full review June 2015.