What the most accurate test is: creatine kinase-MB or troponin?
Your body makes 3 forms of CK, including CK-MB.
- CK-MM (found in skeletal muscles and the heart)
- CK-MB (found mostly in the heart, but small amounts found in skeletal muscles)
- CK-BB (found mostly in the brain and smooth muscle, such as the intestines.
The CK-MB isoenzyme exists as 2 isoforms: CK-MB1 and CK-MB2. Normally, the tissue CK-MB1 isoform predominates; thus, the CK-MB2/CK-MB1 ratio is typically less than 1. A result is positive if the CK-MB2 is elevated and the ratio is greater than 1.7.
CK-MB2 can be detected in serum within 2-4 hours after onset and peaks at 6-9 hours, making it an early marker for acute MI.
Creatine kinase in the blood may be high in health and disease. Exercise increases the outflow of creatine kinase to the blood stream for up to a week, and this is the most common cause of high CK in blood.
Finally, high CK in the blood may be an indication of damage to CK-rich tissue, such as in rhabdomyolysis, myocardial infarction, myositis and myocarditis. This means creatine kinase in blood may be elevated in a wide range of clinical conditions including the use of medication such as statins; endocrine disorders such as hypothyroidism; and skeletal muscle diseases and disorders including malignant hyperthermia, and neuroleptic malignant syndrome.
Troponin T is a part of the troponin complex, which are proteins integral to the contraction of skeletal and heart muscles. The cardiac subtype of troponin T is especially useful in the laboratory diagnosis of heart attack because it is released into the blood-stream when damage to heart muscle occurs.
CK-MB and troponin levels both rise at 3-6 hours after the start of chest pain. They have nearly the same specificity. The main difference between CK-MB and troponin is that CK-MB only stays elevated 1-2 days while troponin stays elevated for 1-2 weeks. Therefore, CK-MB is the best test to detect a reinfarction a few days after the initial infarction.
