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MB-fraction of creatine kinase in serum
Last reviewed: 18.10.2021
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Reference values (norm) of activity of MB-fraction of creatine kinase in serum: 6% of total activity of CC or 0-24 IU / l.
Creatine kinase in the cardiac muscle consists of two isoenzymes: KK-MM (60% of total activity) and KK-MB (40% of total activity). KK-MB - dimer, consists of two subunits: M (muscle) and B (cerebral). MB-fraction can not be considered strictly specific for the myocardium. 3% creatine kinase of skeletal muscles are represented by this fraction. Nevertheless, the increase in activity of QC-MB is considered to be the most specific for myocardial infarction - it accounts for more than 6% of the total QC (up to 25%). The increase in activity of CC-MB is observed only 4-8 hours after the onset of the disease, the maximum is reached after 12-24 hours, on the 3rd day the activity of the isoenzyme returns to normal values in the uncomplicated course of myocardial infarction. With the expansion of the myocardial infarction zone, the activity of KK-MB is increased longer, which allows to diagnose a heart attack of prolonged and recurrent course. The maximum activity of KK-MB is often achieved before the maximum activity of total creatine kinase. The degree of increase in the activity of the increase in creatine kinase and KK-MB corresponds to the magnitude of the affected zone of the myocardium. If during the first hours of myocardial infarction the patient was started with thrombolytic therapy, then the peak of activity of creatine kinase and KK-MB may appear earlier than usual, which is explained by faster leaching of the enzyme from the affected area (the result of reperfusion is the restoration of the patency of the thrombosed coronary artery).
In the blood, carboxypeptidase cleaves the terminal lysines of the peptide dimer KK-MB with the formation of the two main isoforms: KK-MB 1 and KK-MB 2. In the serum of a healthy person, the coefficient of KK-MB 2 / KK-MB 1 is less than or equal to 1.5. After myocardial infarction, the activity of KK-MB 2 increases rapidly and the coefficient of KK-MB 2 / KK-MB 1 becomes greater than 1.5. In clinical practice this coefficient is used for the early diagnosis of myocardial infarction and the onset of reperfusion with thrombolytic therapy.
The carried out researches have shown, that at people at electrophoretic separation kreatokinazy it is possible to reveal 2 types macro-KK. Macro-KK type 1 represents CC-MB associated with IgG, less frequently with IgA. In the case of electrophoresis, macro-KK type 1 is located between the KK-MM and KK-MB. It is found in 3-4% of hospitalized elderly patients, in women more often than in men. This type of creatine kinase can be present in the blood of patients for years and is not associated with any disease. Macro-KK type 2 - mitochondrial creatine kinase (oligomer mitochondrial creatine kinase). With electrophoresis, it migrates to the cathode as a KK-MB. Macro-KK type 2 indicates a serious damage to the cell, it is observed in severe diseases (myocardial infarction, shock, malignant tumors, hepatitis, cirrhosis, severe heart failure) and is a prognostically unfavorable sign.
Various tumors can produce CC-MB or KK-MM, which account for 60% or more of the total creatine kinase activity. In this regard, if the CK-MB is more than 25% of the total creatine kinase, it is necessary to suspect a malignant neoplasm as a reason for increasing the activity of the enzyme.
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