Troponin

Troponin is a complex of three regulatory proteins (troponin C, troponin I and troponin T) that is integral to muscle contraction in skeletal and cardiac muscle, but not smooth muscle. Troponin, working in conjunction with tropomyosin, functions as a molecular switch, regulating muscle contraction in response to changes in intracellular Ca2+ concentration.

Certain subtypes of troponin (cardiac troponin I and T) are very sensitive and specific indicators of damage to the heart muscle (myocardium). They are measured in the blood to differentiate between unstable angina and myocardial infarction (heart attack) in patients with chest pain or acute coronary syndrome. Normal levels of cTn I in the blood are very low. A patient who had suffered from a myocardial infarction would have an area of damaged heart muscle, and would have elevated cardiac troponin levels in the blood. Cardiac TnI has a similar release pattern to CK-MB, the earlier indicator of heart damage; both can be measured 4-6 hours after the onset of pain. The level of cTnI remains elevated for a much longer period of time (6-10 days), which provides a longer window of detection of cardiac injury and allows for the detection of acute myocardial infarction (AMI) much earlier after the onset of ischemia (4 hours). Recent data have identified a measurable relationship between cardiac troponin levels and long-term outcome after an episode of chest discomfort. These studies suggest that the use of the cTnI demonstrates high predictive value in evaluating the high-risk group of unstable angina patients.

Reference:

1. Adams, J. et, al., N. Eng. J. Med., (1994) 330: 670-674. 1994.
2. Cummins B, et al., (1987). "Cardiac-specific troponin-I radioimmunoassay in the diagnosis of acute myocardial infarction". Am Heart J. 113: 1333–1344.
3. Katus, H.A., et al., (1989). "Enzyme linked immunoassay of cardiac troponin T for the detection of acutemyocardial infarction in patients". J Moll Cell Cardiol. 21: 1349–1353.

Selected Troponin Products