Troponin is a protein found within the cells of heart muscle, playing a direct role in muscle contraction. Its presence in the bloodstream is an important indicator of heart health. Measuring troponin levels helps healthcare professionals assess potential damage to the heart muscle.
What is Troponin?
Troponin is a complex of three regulatory proteins—troponin C, troponin I, and troponin T—that are integral to muscle contraction in both skeletal and cardiac muscle. In a relaxed muscle, other proteins block the sites where muscle fibers interact, preventing contraction. When a muscle cell is stimulated, calcium ions are released and bind to troponin C. This binding causes a change in the troponin complex’s shape, which then exposes the binding sites on actin filaments, allowing myosin to attach and initiate muscle contraction.
Troponin is found in both skeletal and cardiac muscle, but cardiac troponin I (cTnI) and cardiac troponin T (cTnT) are specific to heart muscle. These cardiac-specific troponins are measured in blood tests to evaluate heart damage. When heart muscle cells are injured, these proteins leak into the bloodstream, making them detectable biomarkers for cardiac injury.
Normal Ranges and Interpretation
In healthy individuals, troponin levels are very low or undetectable in the bloodstream. Troponin is contained within heart muscle cells and is only released when they are damaged. Even slight increases in troponin can suggest heart damage.
Normal troponin thresholds vary between laboratories and assay types. For high-sensitivity tests, a normal range for troponin I is typically less than or equal to 15 picograms per milliliter (pg/mL) for women and 20 pg/mL for men. For high-sensitivity cardiac troponin T (hs-cTnT), levels above 14 ng/L are considered elevated. Conventional tests may define normal troponin I as 0 to 0.04 ng/mL, with troponin T below 0.01 ng/mL.
When Troponin Levels Are Elevated
Elevated troponin levels indicate heart muscle damage. More severe damage results in higher troponin release. While a heart attack is the most common reason for significantly raised troponin levels, especially when they rise and fall over hours, other conditions can also cause these levels to increase.
Other causes include heart failure, myocarditis (inflammation of the heart muscle), and chronic kidney disease, where reduced clearance can lead to accumulation. Pulmonary embolism, severe infections (like sepsis), and intense physical exercise can also increase troponin. Interpreting elevated troponin levels requires a comprehensive assessment by a doctor, considering symptoms, medical history, and other diagnostic test results.