Function
The entire troponin complex consists of troponin C, I and T. In the skeletal and cardiac muscle, troponin I and T together with the muscle protein tropomyosin act like an applied brake on muscle contraction. This is presumably done by simply covering and thus blocking the interaction sites of the contractile muscle proteins at rest. Only when a muscle receives the signal for contraction via a nerve, this brake is released and muscle movement occurs by shortening the contractile apparatus.
On a microscopic level, this signal is an increase in the calcium concentration in the plasma of the muscle cell. Calcium ions are bound by troponin C, which causes a deformation of the troponin complex, a so-called conformational change. This conformational change causes the entire complex to shift slightly, thereby releasing the interaction sites of the muscle proteins and causing them to contract.
This process takes place in the contracting muscle at millions of sites simultaneously due to the increased calcium concentration in the entire cell plasma. The strength of a muscle contraction is determined by the strength of the incoming nerve impulse. A very strong stimulus causes the calcium concentration to increase more strongly, which deforms almost the entire troponin. This leaves a large number of interaction sites of the contractile apparatus exposed. This causes the muscle to contract more strongly and faster than with a weaker stimulus.
Troponin Test
The troponin test determines the concentration of troponin in the blood. Frequently, only troponin T and I are tested, as these two proteins are specific to the heart muscle, i.e. they are usually only found there. To test the troponin concentration, it is sufficient to draw a small amount of blood, usually from a vein.
Normally, the concentration is tested in blood serum, i.e. the aqueous blood portion. The actual test is carried out with the help of a so-called immunoassay. With this precise method, the troponin concentration can be determined exactly.
Alternatively, there is a rapid test, the function and evaluation of which is similar to a commercially available pregnancy test, but is carried out with blood. However, the rapid test does not allow an exact determination of the concentration, but only detects an increase in troponin above the normal value. The measurement of the troponin concentration is repeated after a period of several hours.
In an acute process, such as a heart attack, a change in the values would be detected. If, on the other hand, both values are similar, the cause of the troponin increase is likely to have existed for a longer period of time. Cardiac troponin hardly occurs in the blood of a healthy adult.
There is therefore no value that is too low. The limit value for a potentially dangerous troponin elevation in the case of troponin T is a concentration of more than 0.1 ng/ml (0.1 μg/l). If a severe heart attack occurs, this value can rise to 90 ng/ml and more.
The situation is similar with the standard value of Troponin I. Here too, the concentration should be below 0.1 – 0.2 ng/ml, while in healthy individuals it is present in barely detectable amounts. An increase in troponin levels can have many reasons.
Very often they can be traced back to damage to the heart muscle. This is the only human tissue in which large amounts of cardiac troponin can be found. Even small damage to the heart muscle therefore causes a measurable increase in troponin levels.
However, a heart attack does not always have to be the cause of an increase in troponin. Even minor circulatory disorders of the heart muscle can result in altered values due to cell damage. Inflammation of the heart muscle, so-called myocarditis or functional disorders of the heart, so-called cardiomyopathies, can also cause increased troponin levels.
If kidney function is poor, there is no filtering of the blood and troponin T can accumulate in the body. If several of these factors come together, the troponin value can be greatly altered without acute damage to the heart muscle, for example through a heart attack. A mere increase in the troponin concentration in the blood is therefore relatively unspecific, but should not occur in completely healthy people. Signs of a myocardial infarction
