Creatine kinase (CK) in cats and dogs
Creatine kinase (CK, also written CPK) is an enzyme inside muscle cells — skeletal and heart muscle — and the brain. When muscle cells are damaged, even slightly, CK leaks into the blood, so it is a very sensitive marker of muscle injury. It also leaves the blood quickly, and outside a specific muscle problem a raised CK often has little clinical meaning.
What it shows
CK sits in the cytoplasm of muscle cells, mainly skeletal and heart muscle, and in the brain. Merck notes that only a very small amount of muscle damage, such as bruising or an intramuscular injection, can produce high serum CK. Its half-life is short — about 2.5 hours in dogs in an experiment cited by eClinPath — so CK drops quickly once the injury stops, while ongoing muscle damage keeps it high.
AST, another enzyme found in muscle, rises more gradually after muscle injury and stays raised longer than CK, so vets read the two together. Merck sums up the practical side: in dogs and cats, unless a specific muscle disease is being investigated, increased CK is generally of no clinical significance.
Higher than reference — what it may be a sign of
- Intramuscular injections: raise CK to varying degrees, depending on how irritating the drug is.
- The blood draw itself: accidental entry of the needle into muscle (a “muscle stick”) can cause 3- to 4-fold increases; eClinPath has seen CK as high as 3,000–4,000 U/L from this alone.
- Hemolysis in the sample: moderate hemolysis may mildly increase the result.
- Lying down for long periods or after surgery: recumbent and post-surgical patients can have CK up to about 10 times normal.
- Exertional muscle damage: Merck describes markedly elevated CK in acute exertional myopathy, which occurs mostly in racing Greyhounds and endurance sled dogs.
- Muscle disease: inherited muscular dystrophies and polymyositis. Merck lists rhabdomyolysis (muscle breakdown) and aortic thromboembolism (a clot blocking the main artery) among causes of marked rises, and slight increases in hypothyroidism.
- Sick cats that are not eating: see the section on cats.
Lower than reference
The clinical pathology references describe causes of high CK, not of low CK; a value slightly below the range is noted and read together with the rest of the panel. Very lipemic (milky) samples are a separate issue: eClinPath lists CK among the results that marked lipemia can affect.
Look at together with
- AST — rises with both muscle and liver damage; next to a high CK it supports a muscle origin.
- ALT — mainly a liver enzyme; reading it next to CK and AST helps separate muscle from liver.
- Creatinine and urea — in severe exertional myopathy Merck describes acute kidney failure secondary to myoglobin in the urine.
- The circumstances of the visit — recent injections, a difficult blood draw, surgery or a long time lying down; worth telling the vet.
Units and conversion
CK is an enzyme, so labs report its activity in units per litre: U/L on English forms, Ед/л or МЕ/л on Russian ones. These are the same unit, so there is nothing to convert. Forms may label it CK or CPK. Reference ranges differ between analysers, so a trend is best followed in one lab.
Reference range
The reference range is on your lab’s form. Vets describe a rise as a multiple of the upper limit: a 3–4-fold rise can come from the blood draw alone, while eClinPath calls rises above 30 times the upper limit marked. Because CK leaves the blood within hours, the vet may repeat it to see whether the rise persists — persistent or ongoing muscle injury keeps CK high, a one-off event does not.
Cats and dogs
CK is often raised in sick cats. In a study cited by eClinPath, 60% of cats with various diseases had increased CK, but marked increases (over 30 times the upper limit) were seen in only 7%, and some of them may have come from muscle sticks. Critically ill cats that were not eating had a median CK of 2,500 U/L, higher than healthy cats; CK declined as the illness resolved.
In dogs CK leaves the blood quickly (half-life about 2.5 hours in the experiment cited by eClinPath), so a rise caused by an injection or a difficult draw fades fast. Hard physical work matters for working breeds: acute exertional myopathy occurs mostly in racing Greyhounds and endurance sled dogs, with markedly high CK and, in severe cases, a risk to the kidneys.
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.