The CK test measures the level of creatine kinase, an enzyme found in muscle cells. Elevated CK levels may indicate muscle damage or injury, such as muscular dystrophy, myocardial infarction, or rhabdomyolysis, and can lead to symptoms like muscle pain, weakness, and dark urine. While low CK levels are rare and typically not clinically significant, they may occur in conditions such as severe malnutrition or muscle wasting disorders.