Creatine kinase-MB (CPK-MB)

Why this test?

For the diagnosis of acute myocardial infarction in the first hours after the onset of symptoms.

For differential diagnosis of diseases accompanied by pain in the pericardial region.

To assess the degree of damage to the myocardium and to make a prognosis of the disease, including when exposed to large doses of ethanol, acute and chronic carbon monoxide poisoning.

For the diagnosis of recurrent heart attack.

To assess the degree of risk of myocardial infarction and other coronary disorders in patients in the rehabilitation period after major cavity and other surgical operations.

To assess complications when prescribing cerivastatin, fluvastatin and pravastatin.

In what cases is it prescribed?

With symptoms of acute coronary syndrome: intense chest pain lasting more than 30 minutes, which is not eliminated by nitroglycerin, weakness, sweating, shortness of breath with minimal physical exertion.

With symptoms of acute coronary syndrome without characteristic changes in the electrocardiogram.

With symptoms of acute (and chronic) myocarditis: vague chest pain, increased fatigue, feeling of interruptions in the work of the heart.

When monitoring the function of the myocardium in the early post-infarction period.

Assessment of the degree of damage to the myocardium and when making a prognosis of the disease, including long-term exposure to large and small doses of ethanol and carbon monoxide.

Test information

Creatine kinase MB (CK-MB) is an isoform of the enzyme creatine kinase, which is involved in the energy exchange of cells.

Creatine kinase consists of two subunits: M (from English Muscle - «muscle») and B (from English Brain - «brain»). Combinations of these subunits form the CK-BB, CK-MM, and CK-MB isoforms of creatine kinase. As a result of damage to the cell membrane due to hypoxia or other reasons, these intracellular enzymes enter the systemic bloodstream and their activity increases.

While CK-MM and CK-BB isoforms predominate in muscle and nerve tissue, creatine kinase MB is almost entirely found in cardiac muscle. It is present in very small amounts in the blood of a healthy person. Therefore, an increase in the activity of creatine kinase MB is a highly specific and sensitive indicator of myocardial damage.

Damage to the myocardium can occur due to various factors, such as trauma, dehydration, infectious disease, exposure to heat and cold, and chemicals.

However, its main cause is atherosclerosis of coronary vessels and coronary heart disease (CHD).

Ischemic heart disease has several forms. The test for creatine kinase MB is most often used in acute myocardial infarction (MI). In the blood of a person experiencing an acute myocardial infarction, the activity of creatine kinase MB can be increased within 4-8 hours after the onset of symptoms of the disease, the peak occurs at 24-48 hours, and the indicator usually returns to normal by the 3rd day. This makes it possible to use creatine kinase MB to diagnose not only primary MI, but also recurrent infarction (for comparison: troponin I and lactate dehydrogenase LDH normalize by approximately the 7th day).

It should be noted that the rate of change in MB creatine kinase activity depends on many reasons: previous myocardial pathology, the presence or absence of heart failure, etc. Therefore, for the most accurate diagnosis, repeated measurements of MB creatine kinase activity are required at intervals of 8-12 hours during the first 2 days after the onset of disease symptoms. MB creatine kinase activity may remain normal for the first 4-8 hours even after a heart attack has occurred.

There is a direct relationship between the activity of creatine kinase MB and the prevalence of heart attack, and therefore this indicator can be used in making a prognosis of the disease.

Ischemic damage to the myocardium, which does not lead to the development of a heart attack (for example, stable angina pectoris), as a rule, does not increase the activity of creatine kinase MB.

At a time when ischemic heart disease usually affects people of mature age and older people, myocarditis prevails among young people. Most often, it is caused by the cardiotropic virus Coxsackievirus (although it is usually impossible to establish the cause). A patient with myocarditis feels vague retrosternal pain, increased fatigue, interruptions in the work of the heart.

The nature of these symptoms changes during the day and with physical exertion. However, they are rarely very pronounced, and because of this, the disease often remains unrecognized. Inflammation in the myocardium eventually leads to irreversible changes: dilated cardiomyopathy and congestive heart failure. An increase in creatine kinase MB is noted in the case of large myocardial involvement in myocarditis. In contrast to acute myocardial infarction, in myocarditis the activity of creatine kinase MB is characterized by a steady and long-term increase.

Rare but dangerous Reye's syndrome, which occurs more often in children of younger preschool age, also occurs with damage to the heart muscle. The development of this disease is facilitated by the use of aspirin and a viral infection, most often it is herpes zoster (chicken pox in children) or the flu. With this syndrome, liver function is significantly impaired, cerebral edema and acute encephalopathy occur.

Other myocardial diseases, such as heart failure, cardiomyopathy, rhythm disturbances, in most cases do not lead to a significant increase in the activity of creatine kinase MB.

Some substances have a direct toxic effect on the myocardium: alcohol intake contributes to a 160-fold increase in the activity of creatine kinase MB, acute and chronic CO poisoning - 1000-fold.

Insignificant activity (less than 1%) of creatine kinase MB is observed in muscle tissue. Therefore, with extremely high physical exertion (for example, marathon running) or with a large trauma of the skeletal muscles, the activity of creatine kinase MB may increase slightly even without damage to the myocardium.