A troponin test measures the level of troponin in the blood, a type of protein found in the muscles of the heart. Troponin isn't normally found in the blood, but when heart muscles are damaged, troponin is send into the bloodstream. As heart damage increases, greater amounts of troponin are released into the blood.
High levels of troponin in the blood may indicate having/having had a heart attack (recently). Cardiac troponin (cTn) is composed of three different subunits:
- Troponin C (cTnC): binds to calcium ions to produce a conformational change in TnI
- Troponin T(cTnT): binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex
- Troponin I (cTnI): binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place
cTn is present in myocardial cells in the form of the cTnI-C-T complex and free cTnI, which is released into blood circulation when an acute myocardial infarction (AMI) occurs. Then, cTnI-C-T can be further decomposed into the cTnI-C complex and free cTnT, where the cTnI-C complex is the main form in the blood.
Most quick immunochemical Troponin Tests are lateral flow chromatographic immunoassays used for the qualitative detection of cardiac Troponin I (cTnI) in human serum, plasma or whole blood at a level ≥1ng/mL. This test is very useful in the diagnosis of AMI.
Normally, the level of cTnI in the blood is very low. cTnI is released into the blood stream in forms of free cTnI and cTnI-C-T complex at 4-6 hours after myocardial cell damage. The elevated level of cTnI could be as high as 50ng/mL during 60-80 hours after AMI and remains detectable for up to 10-14 days post AMI. Therefore, cTnI is a specific and sensitive marker for AMI.
Work procedure for the troponin tests differ from one test device manufacturer to another. Some tests use the: 2 drops of serum/plasma plus 1 drop of buffer or 5 microliters serum plus 2 drops of buffer (it may also be the case that the test cassette already contains what it needs so no buffer is added, only the sample from the patient). Below is an example of a work procedure for the troponin test:
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