Troponin

and Eva Rudolf-Müller, doctor

Florian Tiefenböck studied human medicine at the LMU Munich. In March 2014, he joined as a student and has supported the editorial team with medical articles ever since. After receiving his medical license and practical work in internal medicine at the University Hospital Augsburg, he has been a permanent member of the team since December 2019 and, among other things, ensures the medical quality of the tools.

What is troponin?

Troponin is an important muscle protein: skeletal and heart muscles are made up of muscle fibers (myocytes, muscle fiber cells), albeit in different ways. Each muscle fiber consists of up to hundreds of muscle fibrils (myofibrils) that contain thread-like strands (myofilaments). There are various proteins on these strands that help the muscles contract and relax again. One of these proteins is troponin.

What is troponin exactly?

There are basically three different troponins. They are made up of amino acids and form protein complexes. These each consist of three sub-units. The subunit (UE) troponin C binds calcium. The UE Troponin T docks to another protein (tropomyosin), as does the UE Troponin I, which is attached to the structural protein actin. Their interaction enables muscles to contract and relax again. The body's three troponin complexes are:

the heart troponin (consists of the subunits cTnT, cTnI, TN-C)
the troponin of the white skeletal muscles (for fast movements, consists of the UE fTnT, fTnl, TN-C2)
the troponin of the red skeletal muscles (for strength endurance, consists of the UE sTnT, sTnI, TN-C).

Importance in medicine

In medicine, the determination of muscle protein is aimed specifically at the two protein complexes troponin T (cTnT = cardiac troponin T) and troponin I (cTnI = cardiac troponin I), which only occur in heart muscle cells. Experts therefore count them among the so-called biomarkers. Biomarkers are the body's own substances (such as proteins or metabolic products) that are suitable for making statements about disease processes in the body. In the case of a heart attack, for example, troponin serves as a biomarker for heart damage.

When is troponin determined?

If the doctor suspects that a patient's heart muscle is damaged, he determines troponin T and troponin I (he also makes a so-called 12-lead ECG). In addition to these two laboratory values, the doctor also has other endogenous substances measured, which are increased after a heart attack. These include various protein structures such as myoglobin and the enzymes creatine kinase (CK and CK-MB), lactate dehydrogenase (LDH) and glutamate oxaloacetate transaminase (GOT = AST). However, these substances are also found in other body cells and are therefore not heart-specific. In everyday clinical practice, doctors summarize the substances mentioned under the term "cardiac enzymes".

In addition, doctors determine troponin to uncover a rejection reaction after a heart transplant. They also determine the troponin value for heart muscle damage caused by organ failure elsewhere (especially the kidney).

Troponin test

To measure troponin, the doctor takes a blood sample from the patient, which is then analyzed in the laboratory.

In addition, there are also troponin tests that can be carried out directly on the patient's bed. Since their results are often less precise than the measured values from the laboratory, they are primarily used to check the course of the measured values.

Thanks to more recent developments, there are now even more sensitive test procedures, so-called highly sensitive troponin T tests. With this troponin T hs (hs = highly sensitive) an acute myocardial infarction can be detected even earlier than before. Because with conventional tests it is difficult to detect muscle protein shortly after a heart attack (increase only measurable after about three hours).

Troponin test for heart attack

A heart attack (myocardial infarction) occurs when a blood vessel in the heart (coronary artery or coronary artery) narrows too much or closes completely due to deposits on the inner walls. The heart muscle is then no longer (sufficiently) supplied with oxygen and can no longer do its work. Patients experience a strong feeling of pressure, burning or pain behind the breastbone (angina pectoris), possibly radiating to the arms, neck, jaw, upper abdomen or back.

If a heart attack is suspected, doctors will perform an electrocardiogram (EKG) as soon as possible. If changes that are typical of an infarction (such as so-called ST elevations), they initiate measures to restore blood flow to the coronary vessels (revascularization).

If the ECG does not show any abnormalities, a heart attack cannot yet be ruled out (for example in the case of a so-called NSTEMI). In this case, troponin comes into play as the most important infarct biomarker. However, since it only increases after a while (and can therefore still be normal shortly after a possible heart attack), doctors check the blood level of the heart muscle protein several times at short intervals. Doctors use troponin T hs tests, as these can indicate heart muscle damage very early on.

Control of the course

Troponin increases in the first few hours after heart damage. It peaks in around 12 to 96 hours. It takes about six days to two weeks for the values to recover. That is why doctors also determine the heart muscle protein in order to check the course of a heart muscle disease or the success of a therapy (such as revascularization).

Troponin normal values

Which troponin norm values apply depends on the test procedure. Highly sensitive tests can detect even the smallest amounts of heart muscle protein in the blood. Therefore, there are different troponin T norm values than in conventional examination methods.

	Troponin T / Troponin I.	Troponin T hs (highly sensitive)
Normal values	<0.4 µg / L	<14 ng / L (<0.014 µg / L) (<0.014 ng / ml; <14 pg / ml)
Suspected heart muscle disease, infarction cannot be ruled out	0.4 - 2.3 µg / L	14-50 ng / L (0.014-0.05 µg / L) (0.014-0.05 ng / ml; 14-50 pg / ml)
Suspected heart attack	> 2.3 µg / L	> 50 ng / l (> 0.05 µg / L) (> 0.05 ng / ml;> 50 pg / ml)

When are the troponin levels lowered?

Troponin is found in the heart muscle cells. It is only released when these are damaged. Therefore, the heart muscle protein is usually not detectable in the blood of healthy people. Sometimes there are slightly raised values due to measurement technology (but still within the normal values).

When are the troponin levels increased?

Even slightly damaged heart muscle cells lead to an increase in troponin levels. The reasons for these increased values are:

Heart attack (myocardial infarction), general: Acute coronary syndrome (unstable angina pectoris, NSTEMI, STEMI)
Palpitations with arrhythmias (tachycardiac arrhythmias)
dangerous rise in blood pressure (hypertensive crisis)
Heart failure (heart failure)
Inflammation of the heart muscle (myocarditis)
Heart muscle diseases such as Tako Tsubo cardiomyopathy (malfunction due to psychological or emotional stress, also called "broken heart" syndrome)
Tear of the main artery wall (aortic dissection), severely narrowed main artery (aortic stenosis)
Pulmonary embolism, pulmonary hypertension (= pulmonary hypertension; the blood backlog in the heart causes damage there)
Heart surgeries, heart transplants

Other factors are less likely to cause a patient's blood to have high troponin levels. Among other things, the following reasons lead to an increase in troponin T, especially in highly sensitive tests:

Cramping of the coronary arteries (coronary spasm)
Inflammation of the blood vessels in the heart (coronary vasculitis)
neurological disease events such as stroke or cerebral haemorrhage
slight damage to the heart due to medical interventions such as bypass surgery, cardiac catheters, pacemaker excitation, electric shock (for resuscitation or normalization of the heart rhythm = cardioversion)
Underactive thyroid (hypothyroidism) and overactive thyroid (hyperthyroidism)
drugs that damage the heart (e.g. chemotherapy drugs such as doxorubicin)
Poisons (such as snake venom)
Blood poisoning (sepsis)

What to do if the troponin is changed

Changed or increased troponin values must always be viewed critically. They indicate damaged heart muscle cells. The following applies: the higher the blood level of myocardial protein, the higher the probability of heart damage and the worse the patient's prognosis. Therefore, when the troponin is elevated, doctors act quickly to avoid serious consequences such as fatal cardiovascular failure. They also take blood at regular intervals in order to check the course of the disease and the success of the therapy based on the troponin level.

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