What is a creatine kinase (CK) test? This test measures the amount of creatine kinase (CK) in the blood. High amounts of CK are released into the blood when there is muscle damage. What is this test? This test measures the amount of an enzyme called creatine kinase (CK) in your blood. Creatine kinase, also known as creatine phosphokinase or phosphocreatine kinase, is an enzyme expressed by various tissues and cell types. Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test. CK is found predominantly in the heart muscle, skeletal muscle, and brain and are elevated when these muscle or nerve cells are injured.