What does an elevated creatine kinase (CK) level of 90 indicate regarding myocardial infarction (heart attack)?

Interpretation of Creatine Kinase (CK) Level of 90 in Relation to Myocardial Infarction

A creatine kinase (CK) value of 90 alone is not sufficient to diagnose a myocardial infarction and requires additional context including clinical symptoms, ECG changes, and preferably cardiac troponin measurements for proper interpretation.

Understanding Cardiac Enzymes and Myocardial Infarction

• Creatine kinase (CK) is not recommended as a primary biomarker for diagnosing myocardial infarction due to its lack of specificity, as it is widely distributed in skeletal muscle and other tissues 1
• Current guidelines strongly recommend cardiac troponins (I or T) as the preferred biomarkers for detecting myocardial injury due to their nearly absolute myocardial tissue specificity and high sensitivity 1
• If troponin assays are not available, CK-MB (measured by mass assay) is the best alternative, not total CK 1

Interpreting a CK Value of 90

• A single CK value of 90 cannot be interpreted without knowing:

  • The laboratory's specific reference range and 99th percentile upper reference limit (URL) 1
  • Whether this represents a rise or fall from previous measurements 1
  • The timing of the sample in relation to symptom onset 2
  • Clinical symptoms and ECG findings 1

• Total CK levels can be elevated for many non-cardiac reasons including:

  • Skeletal muscle injury or exertion 1
  • Stroke 3
  • Renal failure 4
  • Various other conditions affecting muscle tissue 1

Current Diagnostic Approach for Myocardial Infarction

• The diagnosis of myocardial infarction requires:

  1. Detection of a rise and/or fall of cardiac biomarkers (preferably troponin) with at least one value above the 99th percentile URL 1
  2. Clinical evidence of myocardial ischemia (symptoms, ECG changes, imaging evidence) 1

• For proper evaluation of suspected myocardial infarction:

  • Blood samples should be drawn at first assessment and 6-9 hours later 1, 2
  • An additional sample between 12-24 hours may be required if earlier measurements were not elevated but clinical suspicion remains high 1, 2
  • The pattern of rise and fall is essential to distinguish acute myocardial injury from chronic elevations 1, 2

Limitations of CK in Myocardial Infarction Diagnosis

• Total CK has poor specificity for cardiac injury compared to troponin or CK-MB 1
• CK may be normal in the early hours (less than 4 hours) after symptom onset even in patients with confirmed myocardial infarction 5, 6
• CK can be falsely elevated in hemodialysis patients and other conditions without myocardial injury 4
• The American College of Cardiology and European Society of Cardiology explicitly state that measurement of total CK is not recommended for the diagnosis of myocardial infarction 1

Practical Recommendations

• If myocardial infarction is suspected, request cardiac troponin testing rather than relying on CK 1
• Serial measurements of cardiac biomarkers are essential to detect the characteristic rise and/or fall pattern 1, 2
• Always interpret biomarker results in the context of clinical presentation, ECG findings, and timing from symptom onset 1
• A normal CK value within 4 hours of symptom onset does not rule out myocardial infarction 5, 6