Serum troponin testing is currently the most widely used and most definitive markers of myocyte injury. In addition, new high-sensitivty troponin assays are now available that are more than ten times as sensitive as the troponin assays of the 1990s and early 2000s.
What is troponin?
The troponin class of proteins are all contractile proteins that regulate muscle contractions; they work with calcium ions and another protein called tropomyosin. There are three types of troponin isoforms:
- Troponin C -- Calcium-binding component
- Troponin I -- Inhibitory component
- Troponin T -- Tropomyosin-binding component
Isoforms of the troponins are found in cardiac muscle and in slow-twitch and fast-twitch skeletal muscles.
- Troponin C is found in both cardiac and skeletal muscle in the same form.
- Troponin I has a specific form found in cardiac muscle, cTnI
- Troponin T also has a cardiac-specific form, cTnT.
Unlike the CK enzymes, troponins are much more specific to myocardial tissue, making them a superior marker for cardiac testing. If cTnI or cTnT are detected in the serum, we can be fairly certain myocardial damage is present. Consequently, CK-MB testing has largely been replaced with troponin testing. Many argue that CK-MB testing should, in fact, now be considered obsolete.