The creatine kinase MB isoenzyme test is part of the tests that are conducted to check for a specific case of cardiac disease, mostly myocardial infarction. Creatine kinase is an enzyme that is used in cells to create a substance called phosphocreatine, which is an energy source in muscle. The whole process works in the following way. Our bodies use the energy from the metabolism of carbohydrates and fats and then store some of that energy in a complex molecule called Adenosine triphosphate or ATP. ATP is then broken down by the enzyme ATPase into adenosine diphosphate ADP whenever the body requires to suddenly use the energy. The conversion from ATP to ADP releases energy while the reconversion uses energy. Creatine plays a role in this equation as well. In muscles and the brain, a substance called phosphocreatine is a quick energy source that be used within 7 seconds of ATP completely draining away. Phosphocreatine is created from the reaction of ATP being broken down into ADP and the extra phosphorus ion creating phosphocreatine. This conversion is done by creatine kinase. The reaction is reversible as well.
Creatine kinase comes in isoforms or isoenzymes for various functions. Creatine kinase MB isoenzyme in plasma is one of the markers that are used to check for cardiac defects. Creatine kinase MB isoenzyme in serum is highly unlikely to be found, but one of the other isoforms of it can sometimes be rarely found. The presence of the enzyme in elevated levels in the blood is useful in cardiac tests because the heart is one bug muscle that is continuously working and is always performing the energy reaction of ATP to ADP, and phosphocreatine to ATP. This means that both creatine kinase and phosphocreatine are found in the muscles of the heart. When this starts to appear in higher than normal levels in the blood, it is a sign that a heart muscle is damaged; a condition called myocardial infarction.
This does not mean that the problem is only limited to the heart. The elevated levels in the creatine kinase test could also indicate massive muscular destruction, as is seen in muscular dystrophy, inflammations in muscles, injury, muscular degradation, and even renal failure because the kidneys are the site of creatine production after which phosphocreatine is created in the liver, and then transported to the muscles for storage and use, whenever it is needed for a quick rush of power.