What does an elevated Creatine Kinase (CK) level indicate in a patient with chest pain?

Elevated Creatine Kinase (CK) in Chest Pain: Diagnostic Implications

With the availability of cardiac troponins, elevated creatine kinase (CK) alone is not useful for the diagnosis of acute myocardial injury in patients with chest pain. 1 Current guidelines clearly state that troponins have replaced CK and CK-MB as the preferred biomarkers for diagnosing myocardial injury.

Understanding CK Elevation in Chest Pain

Elevated CK in a patient with chest pain can indicate several conditions:

Cardiac Causes:

• Myocardial injury: While troponins are more specific and sensitive, CK (particularly CK-MB isoenzyme) can be elevated in myocardial damage
• Severity indicator: Higher CK-MB/CK ratios may reflect the extent of coronary disease 2
• Potential marker of prognosis: Elevated CK-MB has been associated with increased risk of cardiac events 3

Non-Cardiac Causes:

• Skeletal muscle injury: CK is present in skeletal muscle and can be elevated due to trauma, intramuscular injections, or excessive exercise
• Rhabdomyolysis: Significant muscle breakdown leads to marked CK elevation
• Other conditions: Hypothyroidism, seizures, and certain medications can cause CK elevation

Current Diagnostic Approach

The 2021 AHA/ACC guidelines for chest pain evaluation clearly state:

1. Troponins are preferred: "High-sensitivity cTn is the preferred biomarker because it enables more rapid detection or exclusion of myocardial injury and increases diagnostic accuracy" 1

2. CK-MB is obsolete: "With availability of cTn, creatine kinase myocardial (CK-MB) isoenzyme and myoglobin are not useful for diagnosis of acute myocardial injury" 1

Clinical Implications

When evaluating a patient with chest pain and elevated CK:

• Obtain troponin measurements: Serial cardiac troponin I or T levels are essential to identify myocardial injury 1

• Consider non-cardiac causes: If troponins are normal but CK is elevated, investigate skeletal muscle causes

• Look for ECG changes: Integrate ECG findings with biomarker results to determine if ACS is present 1

• Consider additional testing: In patients with elevated CK but normal troponins and non-diagnostic ECG, consider:

  • Stress testing (exercise or pharmacological)
  • Cardiac imaging (echocardiography, cardiac MRI)

• Remember timing: CK rises within 4-6 hours after myocardial injury and returns to normal within 24-36 hours, while troponins remain elevated for 4-14 days 4

Special Considerations

• Cocaine use: Can cause elevated CK and CK-MB due to increased motor activity and muscle injury without myocardial infarction 4

• Unexplained troponin elevation: In patients with elevated troponin but unobstructed coronary arteries, cardiac MRI can help diagnose conditions like myocarditis (60%), takotsubo cardiomyopathy (14%), or myocardial infarction with normal coronaries (16%) 5

• Risk stratification: While CK-MB was historically used for risk stratification, current guidelines recommend using troponins for this purpose due to their superior cardiac specificity and sensitivity 4

Pitfalls to Avoid

• Relying solely on CK: Do not use CK or CK-MB alone for diagnosis of myocardial injury
• Ignoring troponin: Even small elevations of troponin indicate increased risk and should not be dismissed
• Missing non-cardiac causes: Elevated CK with normal troponin should prompt investigation for non-cardiac causes
• Delaying diagnosis: Serial measurements of troponin should be obtained at 3-6 hour intervals to avoid missing evolving myocardial injury

In summary, while elevated CK in chest pain patients may suggest myocardial injury, current guidelines emphasize that troponin measurements have replaced CK and CK-MB as the preferred biomarkers for diagnosing acute myocardial injury due to their superior cardiac specificity and sensitivity.