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), which contain thread-like strands (myofilaments). These strands contain various proteins that help the muscles to contract and relax again. One of these proteins is troponin.
What exactly is troponin?
There are basically three different troponins. They are made up of amino acids and form protein complexes. These each consist of three subunits. The subunit (UU) troponin C binds calcium. The troponin T subunit binds to another protein (tropomyosin), as does the troponin I subunit, which binds to the structural protein actin. Their interaction enables muscles to contract and relax again. The three troponin complexes of the body are
- cardiac troponin (consists of the subunits cTnT, cTnI, TN-C)
- the troponin of the white skeletal muscles (for fast movements, consists of the subunits fTnT, fTnl, TN-C2)
- the troponin of the red skeletal muscles (for strength endurance, consists of the UE sTnT, sTnI, TN-C).
Significance in medicine
When is troponin determined?
If the doctor suspects that a patient’s heart muscle is damaged, he will determine troponin T and troponin I (he will also carry out a so-called 12-lead ECG). In addition to these two laboratory values, the doctor will also measure other endogenous substances that are elevated 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 specific to the heart. In everyday clinical practice, doctors summarize these substances under the term “cardiac enzymes”.
Doctors also determine troponin to detect a rejection reaction after a heart transplant. They also determine the troponin value in cases of heart muscle damage caused by organ failure elsewhere (particularly in the kidneys).
Troponin test
To measure troponin, the doctor takes a blood sample from the patient, which is then analyzed in the laboratory.
There are also troponin tests that can be carried out directly at the patient’s bedside. As their results are often less accurate than the measured values from the laboratory, they are mainly used to monitor the course of the measured values.
Troponin test for myocardial infarction
A heart attack (myocardial infarction) occurs when a blood vessel in the heart (coronary vessel) becomes too narrow or completely blocked due to deposits on the inner walls. The heart muscle is then no longer (sufficiently) supplied with oxygen and can no longer perform 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 carry out an electrocardiogram (ECG) as soon as possible. If there are changes typical of a heart attack (such as so-called ST elevations), they initiate measures to restore blood flow to the coronary arteries (revascularization).
If the ECG shows no abnormalities, a heart attack cannot yet be ruled out (e.g. in the case of a so-called NSTEMI). In this case, troponin comes into play as the most important infarct biomarker. However, as it only rises after some time (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 myocardial damage at a very early stage.
Monitoring the progression
Troponin standard values
Which troponin standard values apply depends on the test procedure. Highly sensitive tests can detect even the smallest amounts of cardiac muscle protein in the blood. This is why the troponin T standard values are different from those of conventional test 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 myocardial 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 myocardial infarction |
> 2.3 µg/L |
> 50 ng/l (> 0.05 µg/L) (> 0.05 ng/ml; > 50 pg/ml) |
When are troponin levels low?
Troponin is found in the heart muscle cells. It is only released when these are damaged. Therefore, the heart muscle protein is generally not detectable in the blood of healthy people. Sometimes slightly elevated values are found for measurement reasons (but still within the normal values).
When are troponin levels elevated?
Even slightly damaged heart muscle cells lead to an increase in troponin levels. Causes for these elevated values are
- Heart attack (myocardial infarction), generally: Acute coronary syndrome (unstable angina pectoris, NSTEMI, STEMI)
- Heart palpitations with arrhythmia (tachycardic arrhythmia)
- Dangerous rise in blood pressure (hypertensive crisis)
- Heart failure (cardiac insufficiency
- Heart muscle diseases such as Tako-Tsubo cardiomyopathy (malfunction due to psychological or emotional stress, also known as “broken heart” syndrome)
- Tearing of the aortic wall (aortic dissection), severely narrowed aorta (aortic stenosis)
- Pulmonary embolism, pulmonary hypertension (= pulmonary hypertension; blood backflow into the heart causes damage there)
- Heart operations, heart transplants
Less frequently, other factors are the reason why the troponin in a patient’s blood is elevated. Among other things, the following reasons lead to an increase in troponin T, especially with highly sensitive tests:
- Spasm of the coronary arteries (coronary spasm)
- Inflammation of the coronary vessels (coronary vasculitis)
- Neurological disease events such as stroke or cerebral hemorrhage
- minor damage to the heart due to medical interventions such as bypass surgery, cardiac catheterization, pacemaker stimulation, electric shock (for resuscitation or to normalize the heart rhythm = cardioversion)
- Underactive thyroid gland (hypothyroidism) and overactive thyroid gland (hyperthyroidism)
- heart-damaging medication (e.g. chemotherapeutic agents such as doxorubicin)
- Poisons (such as snake venom)
- Blood poisoning (sepsis)
