From the Guidelines
A rising creatine kinase (CK) level can indeed indicate both rhabdomyolysis and myocardial infarction, with distinct patterns and magnitudes of elevation. In the context of morbidity, mortality, and quality of life, it is crucial to differentiate between these two conditions. According to the most recent and highest quality study, rhabdomyolysis is associated with significantly higher CK levels, often exceeding 5,000-10,000 U/L, whereas myocardial infarction typically presents with more modest CK elevations, 2-10 times the upper limit of normal 1.
When evaluating elevated CK levels, clinicians should consider the clinical context, including symptoms, other laboratory findings, and risk factors. For instance, measuring CK isoenzymes, such as CK-MB, can provide greater specificity for cardiac damage, while total CK predominantly reflects skeletal muscle injury 1. The timing of CK elevation also differs between the two conditions, with MI levels beginning to rise 4-6 hours after cardiac injury, peaking at 24 hours, and normalizing within 48-72 hours.
Key considerations for clinicians include:
- Clinical presentation, including symptoms and physical exam findings
- ECG results
- Laboratory findings, such as CK and CK-MB levels
- Risk factors for rhabdomyolysis and myocardial infarction
- Serial sampling of biomarkers to determine the timing and magnitude of elevation
By considering these factors and interpreting CK levels in the context of the clinical presentation, clinicians can determine whether the elevation suggests rhabdomyolysis, myocardial infarction, or potentially both conditions occurring simultaneously, ultimately guiding treatment decisions to improve patient outcomes.
From the Research
Rising Creatine Kinase Levels
A rising creatine kinase (CK) level can indicate both rhabdomyolysis (rhabdo) and myocardial infarction (MI). The following points highlight the relationship between CK levels and these two conditions:
- Elevated CK levels can be found in patients with either skeletal muscle damage or myocardial infarction 2.
- A maximal CKMB index exceeding 5.0 is diagnostic of myocardial infarction, while a maximal value lower than 3.0 virtually excludes this diagnosis 2.
- Rhabdomyolysis can also cause elevated CK levels, and a peak CK level of at least 5000 U/l is 55% specific and 83% sensitive for the prediction of acute kidney injury requiring renal replacement therapy 3.
Differential Diagnosis
To differentiate between rhabdomyolysis and myocardial infarction, the following points can be considered:
- The CKMB index can be a valuable diagnostic tool in the differential diagnosis of myocardial infarction versus muscle damage 2.
- A McMahon score of at least 6 calculated on admission allows for a more sensitive, specific, and timely identification of patients who may benefit from high-volume fluid resuscitation 3.
- Prolonged cardiopulmonary resuscitation involving repeated cardioversion may predispose to myoglobinuric renal failure, which can be associated with rhabdomyolysis 4.
Clinical Implications
The clinical implications of rising CK levels are:
- Elevated total CK levels have a sensitivity of only 38% and specificity of only 80% for diagnosing myocardial infarction, whereas a CK-MB level over 5% of an elevated total CK level has a sensitivity of only 34% and specificity of 88% 5.
- The content of CK-MB relative to total CK in myocardial cells is variable and can be influenced by preexisting coronary heart disease and medication 6.
- Treatment with beta-blockers before infarction can result in lower relative CK-MBm peak values 6.