Cardiac Troponin I Test

The serum troponin I (cTnI) test measures the level of a specific cardiac regulatory protein. This protein is found almost exclusively in cardiac muscle fibers (cardiac muscle cells) and is released into the bloodstream only when these cells are damaged, such as in an acute myocardial infarction (heart attack). Due to its high sensitivity and specificity for the heart, it has replaced older enzymes (such as CK-MB) as the gold standard for diagnosing a heart attack.