CK (creatine kinase)

CK (creatine kinase) is a muscle-cell enzyme that enters blood from strained or damaged muscles. The test measures total blood CK activity and is performed for muscle pain or weakness, with medicines such as statins, after injuries and when muscle disease is suspected.

Who the test is for

• people with unexplained muscle pain, cramps or weakness;
• people taking statins, cholesterol-lowering medicines, who have muscle symptoms;
• people with suspected inflammatory or inherited muscle disease, such as polymyositis, dermatomyositis or muscular dystrophy, and to monitor these conditions;
• people after serious injury, muscle crushing or lying for a prolonged period after a fall;
• athletes, as an indicator of muscle strain.

What CK is and what it shows

CK is most abundant in skeletal muscle, with less in heart muscle and the brain. A small amount is always in blood; CK rises when muscle cells are damaged or heavily strained. Raised CK therefore indicates something happening in the muscles but does not identify which muscle or why.

CK naturally depends on muscle mass and physical activity: it is higher in men, people with more muscle and athletes, while some healthy people have persistently mildly raised levels without disease. Results are therefore always interpreted alongside symptoms, medicines, recent exertion and other tests.

Preparation and sample

CK is measured in venous blood and fasting is unnecessary. Exertion has the greatest effect: CK rises several hours after training, usually peaks one to three days later, and can remain raised longer after very strenuous or unfamiliar exercise. Avoid intense training, heavy physical work and large amounts of alcohol for at least two to three days before collection.

Mention any recent intramuscular injection, fall or surgery, and which medicines you take, particularly statins. Do not stop medicines yourself.

How to interpret the result

The reference interval depends on sex, age and method and is printed on your report. A doctor interprets the result, if necessary alongside AST, LDH, creatinine and TSH.

Mildly raised CK

This most often results from training, physical work, an intramuscular injection or minor injury. Without symptoms, a doctor usually repeats testing after about a week without strenuous exercise. An underactive thyroid can also raise CK, so TSH is often checked with a raised result.

Markedly raised CK

Several-fold CK elevations occur with severe injuries and crushing, inflammatory and inherited muscle diseases and rhabdomyolysis, the rapid breakdown of muscle cells. Exhausting exertion, particularly in heat, serious injuries, some medicines and alcohol can cause rhabdomyolysis. It is dangerous because the contents of broken-down cells can damage the kidneys.

Seek urgent medical attention if, alongside muscle pain or weakness, you notice dark tea- or cola-coloured urine or pass substantially less urine than usual.

CK with statins

Muscle symptoms with statins are common, while serious muscle damage is rare. A doctor usually requests CK for muscle pain. Normal CK does not rule out statin-related symptoms; a doctor decides on continuing treatment based on symptoms and results. Read more in the article on coenzyme Q10 and statins.

CK and the heart

CK also rises after a heart attack but is no longer used to diagnose it. Heart attacks are established with troponin, a more sensitive test performed in emergency departments and hospitals. For chest pain or pressure, call emergency medical assistance immediately and do not wait for a laboratory test.

Low CK is usually insignificant and most often accompanies lower muscle mass.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list. For athletes, CK is included in Analiza SPORT packages at levels I., III. and IV.

Frequently asked questions

Can training raise CK?

Yes, significantly. After strenuous or unfamiliar training, particularly exercises straining a lengthening muscle, such as downhill running or lowering weights, CK can rise several-fold for several days. Avoiding intense training for several days before collection is therefore important.

What is the difference between CK and CK-MB?

CK-MB is the form of creatine kinase most abundant in heart muscle. It was previously used to diagnose heart attacks but has been replaced by troponin for this purpose. Total CK, measured by this test, primarily reflects skeletal muscles. CK-MB is not measured at Poliklinika Analiza, and total CK is not a substitute.

Is raised CK dangerous?

Mildly raised CK after exertion is usually not dangerous and returns within range after rest. Markedly raised values, recurrent unexplained elevations, muscle weakness or dark urine require attention. A doctor then investigates the cause.

Should I stop my statin if CK is raised?

Not on your own. Stopping treatment increases heart attack and stroke risk. A doctor assesses symptoms and CK level and, if needed, reduces the dose, pauses treatment or changes the medicine.