When to check creatine kinase (CK) levels?

From the Guidelines

Creatine kinase (CK) should be checked in patients with suspected myocardial infarction, particularly when cardiac troponin is not available, as it can help diagnose early infarct extension or periprocedural MI, as stated in the 2012 ACCF/AHA focused update 1. When evaluating patients with suspected muscle damage or disease, CK levels should be checked in patients presenting with unexplained muscle pain, weakness, or tenderness; after trauma or crush injuries; when rhabdomyolysis is suspected; and when monitoring patients on medications known to cause muscle toxicity, particularly statins like atorvastatin or simvastatin. Some key points to consider when checking CK levels include:

• CK should be measured by mass immunoassays, as stated in the 2012 ACCF/AHA focused update 1.
• The use of other, older biochemistry assays of nonspecific markers such as alanine transaminase, aspartate transaminase, and lactate dehydrogenase should generally be avoided in contemporary practice, as recommended by the 2012 ACCF/AHA focused update 1.
• The normal range for CK is typically 30-200 U/L for women and 30-300 U/L for men, though reference ranges may vary by laboratory.
• CK is an enzyme released when muscle cells are damaged, and elevated levels indicate injury to skeletal muscle, cardiac muscle, or brain tissue.
• The degree of elevation can help determine the severity of muscle damage, with mild elevations (3-5 times normal) often seen with medication effects, while massive elevations (>10,000 U/L) suggest severe conditions like rhabdomyolysis that require immediate treatment to prevent kidney damage, as noted in the universal definition of myocardial infarction 1. In terms of specific clinical situations, CK-MB by mass assay is an acceptable alternative when cardiac troponin is not available, as stated in the national academy of clinical biochemistry laboratory medicine practice guidelines 1. Some other situations where CK levels should be checked include:
• After seizures
• In patients with suspected inflammatory or inherited myopathies
• In those with severe exercise-induced muscle damage
• In patients with symptoms of myocardial infarction, as recommended by the national academy of clinical biochemistry laboratory medicine practice guidelines 1. It's also important to note that measurement of total CK is not recommended for the diagnosis of myocardial infarction, because of the large skeletal muscle distribution and the lack of specificity of this enzyme, as stated in the universal definition of myocardial infarction 1.

From the FDA Drug Label

1. 1 Myopathy and Rhabdomyolysis Atorvastatin calcium may cause myopathy (muscle pain, tenderness, or weakness associated with elevated creatine kinase [CK]) and rhabdomyolysis. Discontinue atorvastatin calcium if markedly elevated CK levels occur or if myopathy is either diagnosed or suspected. Inform patients of the risk of myopathy and rhabdomyolysis when starting or increasing the atorvastatin calcium dosage. Instruct patients to promptly report any unexplained muscle pain, tenderness or weakness, particularly if accompanied by malaise or fever.

Check creatine kinase (CK) levels:

• When myopathy is suspected or diagnosed
• If muscle symptoms (pain, tenderness, or weakness) occur, particularly with malaise or fever
• When atorvastatin calcium dosage is increased
• If markedly elevated CK levels occur 2

From the Research

When to Check Creatine Kinase

• Creatine kinase (CK) levels should be checked in patients with suspected acute myocardial infarction (AMI), particularly those who present to the emergency room with chest pain 3, 4.
• CK levels are most useful for diagnosing AMI in patients who present more than 4 hours after the onset of symptoms, as the sensitivity of CK is higher in this population 3, 4.
• CK-MB isoforms can be increased in both acute skeletal muscle injury and MI, but the isoform ratio is most useful for distinguishing recent from old (> 12 h) injury 5.
• In patients with suspected AMI, CK levels should be checked in conjunction with other diagnostic tests, such as electrocardiogram (ECG) and cardiac troponin T, to improve diagnostic accuracy 4, 6.
• CK levels can also be used to predict prognosis in patients with suspected AMI, as elevated CK-MB mass levels are associated with a poor prognosis 6.

Timing of CK Measurement

• CK levels should be measured within 6 hours after the onset of symptoms in patients with suspected AMI, as CK-MB isoforms are increased in most patients with acute skeletal muscle trauma and MI during this time period 5.
• In patients who present more than 4 hours after the onset of symptoms, CK levels can be measured to aid in the diagnosis of AMI, as the sensitivity of CK is higher in this population 3, 4.
• Repeat measurements of CK levels may be necessary to confirm the diagnosis of AMI, as CK levels can fluctuate over time 4.

Clinical Context

• CK levels should be interpreted in the context of clinical presentation, ECG findings, and other diagnostic tests, such as cardiac troponin T and myosin light chains 4, 6.
• Elevated CK levels can be seen in patients with skeletal muscle injury, and the isoform ratio can help distinguish between skeletal muscle injury and MI 5.
• CK levels can be used to monitor the effectiveness of treatment and predict prognosis in patients with AMI 6.