Blood enzymes are proteins that catalyze or accelerate biochemical processes related to the heart or blood. These enzymes may travel through the blood, respond to changes in the chemical composition of the blood, or directly affect blood cells in some way. Some blood enzymes, known as cardiac enzymes, are released from the heart when the heart is damaged; the levels of such enzymes in the blood can be used to diagnose various heart conditions. Levels of other types of enzymes in the blood may indicate damage to the liver, heart, or other organs, so blood analysis aimed at measuring enzyme levels is a common method in medical diagnosis.
Many different blood enzymes exist to ensure that the balance of different substances in the blood remains at a healthy level. Blood sugar levels, for instance, are moderated by many different blood proteins. When blood sugar is too high or too low, changing insulin levels trigger several different blood enzymes to return blood sugar to acceptable levels. Glycogen synthase, which is involved in the conversion of glucose to glycogen, is one such enzyme.
The liver is responsible for many of the body's biochemical processes, including protein synthesis and some aspects of digestion. Many different enzymes are involved in these biochemical processes and are stored in the liver itself. If the liver is damaged in some way, however, it is common for some of these enzymes to enter the bloodstream. Elevated levels of blood enzymes from the liver can be used to diagnose a host of liver conditions. A variety of tests are used to measure the level of the different proteins and can be used to estimate both the structural and functional integrity of the liver.
Heart conditions can similarly be diagnosed based on tests measuring the levels of blood enzymes known as cardiac enzymes or cardiac markers. Such tests, because of issues relating to precision and time, generally cannot be used to conclusively diagnose conditions such as heart attacks while they are happening. They can, however, indicate whether or not a person had or is likely to have a heart attack, and more rapid and precise measurement methods are constantly being developed. The levels of different blood enzymes vary based on how much time passes between heart damage and blood testing. As such, if doctors do not know precisely when the damage occurred, they must often run several tests for different blood enzymes in order to learn anything about the nature of the damage.