When is the CK-MB test done?

CK - Cretine kinase (CK) is an enzyme that catalyzes the reaction that converts creatine to phosphocreatine with the participation of an ATP molecule. There are two polypeptide chains of different origin that combine to form, namely the M chain of muscle origin (musle) and the B chain of brain origin (brain). Therefore, CK has 3 isoenzymes including CK-MB, CK-MM and CK-BB.
CK - MB has a higher percentage in cardiac muscle than in skeletal muscle. CK-MM accounts for about 70% in myocardium and about 25-30% of CK-MB. In healthy subjects, plasma CK is mainly the CK-MM form and a small amount of CK-MB. CK-MB from damaged cardiomyocytes is rapidly released into the bloodstream when the myocardium is damaged. Therefore, the measurement of CK-MB activity is often aimed at detecting myocardial damage. CK-MM mainly occurs in skeletal muscle (98%) and CK-MB only 2%.
CK-BB is found mainly in the brain. Measurement of CK-BB activity is of little clinical use because CK-BB cannot cross the blood-brain barrier to appear in the circulating blood.

The performance of the CK-MB test is aimed at early diagnosis of myocardial infarction. CK-MB activity always increases between 4 and 8 hours after a heart attack. This activity is 10 to 20 times higher than normal, peaks after 15-24 hours and returns to normal after 4-5 days.
Approximately 2⁄3 of the patients still have elevated CK-MB above normal after 72 h. To determine the maximum value, the sample should be tested frequently - approximately every 6 hours. The peak value was higher in elderly myocardial infarction patients than in younger MI patients. Approximately 5% of patients with myocardial infarction (especially elderly patients) have markedly elevated CK-MB activity while CK remains normal. Ck-MB concentration in normal subjects is less than 24U/I.
Compared with other enzymes such as GOT (CK-MB increases after 4 hours, and GOT increases from 6 hours after an infarction), the CK-MB test is significant for early diagnosis of myocardial infarction. However, at present, in small hospitals, because conditions do not allow, GOT test is still used to diagnose myocardial infarction.
Ck-MB levels rise higher than normal if severe musculoskeletal injury occurs. However, such an injury usually does not cause a relative index > 5. CK and CK-MB can also increase if you exercise heavily.
CK-MB levels may also be elevated in people with damaged kidneys without a heart attack. In addition, chronic myopathy, low thyroid hormone and alcohol abuse are also causes of increased CK-MB.
In addition, CK-MB can also be increased in the following cases:
Heart injury Coronary artery spasm Blood stasis Heart failure Myocarditis Heart valve replacement or heart surgery Polymyositis, muscular dystrophy, sarcoma , myoclobinuria or collagen pathology Burning heat or electricity Fever typhus

While testing for LDH and GOT is not necessary because they provide little useful information, an elevated CK-MB test is of decisive diagnostic value. During cardiac surgery, CK-MB levels are also elevated, so that, for about 12-24 hours after surgery, the diagnosis of myocardial infarction cannot be made.
Because hemolysis increases the activity of other enzymes, the CK-MB test is considered the only test of value for the diagnosis of the pathological conditions of myocardial infarction after surgery.

Normal CK – MB index is < 25 U/L.
Total plasma CK concentration in men is from 38 - 174 U/L, in women it is 6 - 140 U/L. The normal plasma CK-MB concentration is < 25 U/L. The normal CK-MB/CK ratio is 2.5 - 3%. To diagnose myocardial infarction, the cut-of value of CK-MB is ≥ 6%.
The half-life of CK-MB in plasma is about 12 hours. The plasma CK-MB concentration usually increases 3 to 6 hours after myocardial infarction. The maximum elevation of CK-MB is after 12-24 hours and then it returns to normal between 48-72 hours after the patient has a myocardial infarction.
If the CK-MB enzyme concentration is high and the CK-MB/CK ratio is ≥ 2.5 - 3%, it is likely that the heart muscle has been damaged. This can occur in the following situations:
Myocardial infarction Acute myocardial damage Myocarditis Inflammation of the endocardium (endocarditis) Pericarditis Unstable angina .... CK and CK-MB values ​​are also elevated in myocardial injury from other causes such as trauma, surgery, or myocardial ischemia. .

Compared with the TnT index (Troponin T), the CK-MB index is more useful in monitoring recurrent myocardial infarction or prolonged infarction because the CK-MB concentration only increases and lasts for 2 - 3 days after myocardial infarction, while TnT can persist for up to 14 days.
Thus, when the test shows that CK-MB has decreased and then immediately increased, it is an early recurrent myocardial infarction. If the CK-MB index increases after 3 days, it is a prolonged myocardial infarction. The combination of both CK-MB/CK and TnT will greatly increase the sensitivity of the diagnosis of myocardial injury.
The CK-MB index does not always accurately reflect damage to the heart muscle. Because there are a number of non-cardiac conditions that can also increase this index such as:
Over-exercising Myasthenia gravis Malignant kidney failure Acute hypothyroidism Alcohol abuse If the CK test is < 80 U/ L does not require further CK-MB testing.
If the CK index test is > 80 U/L, it is necessary to do more CK-MB test and calculate the CK-MB/CK% index to diagnose myocardial damage.
In case of suspicion that the patient has a recurrent myocardial infarction or an ongoing injury, repeat CK and CK-MB tests at 3, 6, and 9 hours after the first test should be performed. .
Another indicator that is CK-MB mass is the concentration of CK-MB as measured by immunoblotting with specific antibodies CK-M and CK-B. This index can be ordered to assess the size of the myocardial infarction.
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