High-sensitivity cardiac troponin

High-sensitivity cardiac troponin is a blood test that measures troponin I or troponin T, proteins associated with heart muscle cells. An elevated level indicates myocardial injury, but on its own it does not reveal the cause nor does it automatically confirm a heart attack. The result is interpreted in conjunction with the patient’s symptoms, the electrocardiogram, the time at which the sample was taken, and changes observed between successive tests.

What is high-sensitivity cardiac troponin and what does it measure?

Cardiac troponins are proteins involved in the contraction of the heart muscle. When heart cells are damaged, some of these proteins may enter the bloodstream.

Laboratories can measure cardiac troponin I or cardiac troponin T. Both can detect myocardial damage, but they are not identical tests: each method uses its own reference ranges, units and interpretation criteria.

The term ‘high-sensitivity’ means that the test can accurately measure very small concentrations of troponin. This makes it possible to recognise certain changes earlier and to use assessment protocols based on multiple measurements.

It does not mean that the test is specific to a heart attack alone. Troponin levels may also rise in other heart conditions and in some general illnesses that affect the heart.

Myocardial injury and heart attack: what is the difference?

This distinction is crucial to understanding the result. Myocardial injury is considered to be present when the troponin concentration exceeds the upper reference limit of the method used.

When several measurements show a significant increase or decrease, this may indicate a recent or acute injury. If troponin remains elevated and changes little, this may correspond to chronic myocardial injury, as occurs in some people with kidney disease, heart failure or certain structural heart conditions.

To diagnose a myocardial infarction, it is not sufficient simply to find elevated or fluctuating troponin levels. There must also be evidence of ischaemia, that is, an insufficient supply of blood and oxygen to the heart muscle.

Such evidence may come from symptoms, an electrocardiogram, imaging tests or other clinical findings.

When should a high-sensitivity troponin test be requested?

It is most commonly used to assess a person with symptoms that may suggest an acute coronary syndrome. These symptoms may include chest pain or tightness, shortness of breath, sweating, nausea, fainting or intense, recently-onset discomfort.

Symptoms vary from person to person. The medical team interprets them in conjunction with the patient’s medical history, physical examination and electrocardiogram. A troponin test may also be ordered in certain situations involving heart failure, myocarditis, pulmonary embolism, sepsis, shock or arrhythmias, where determining the presence and progression of heart muscle damage can provide relevant information.

It may also be measured following certain coronary procedures, heart surgery or trauma. Specific interpretation criteria are used in these contexts. It is not usually used as a general screening test in healthy people without symptoms or a specific clinical concern.

Why it may be necessary to repeat the troponin test

A single measurement does not always indicate whether the injury is recent. Troponin levels change over time. An initial sample may have been taken before the level rises, or it may show an elevation of unknown duration.

Comparing several measurements makes it possible to check whether the concentration is rising, falling or remaining relatively stable.

The interval between samples is not standardised. It depends on the method used by the laboratory, the initial result, the time elapsed since the onset of symptoms, the electrocardiogram and the clinical management protocol.

Some people can be categorised on the basis of just a few measurements. Others require further samples, repeat electrocardiograms, clinical observation or other tests.

How to prepare for a troponin test

Fasting or any special preparation is not usually required. Where an acute heart problem is suspected, the test should not be delayed whilst waiting for any preparation to be completed. It is important to tell the team:

• When the symptoms began, approximately.

• Whether they are continuing, have changed or have disappeared.

• Whether you have kidney disease, heart failure or any other known heart condition.

• Whether you have recently had a serious infection or an arrhythmia.

• Whether you have undertaken any extreme physical exertion.

• Whether you have recently undergone a cardiac procedure.

• Whether previous troponin results are available.

You must not stop taking any medication on your own initiative.

How the cardiac troponin test is carried out

The test requires a blood sample taken from a vein, usually in the arm. In an A&E department, an initial blood sample may be taken shortly after the initial assessment.

The laboratory measures the concentration of troponin I or T using its analytical method and reports the result using the relevant units and reference ranges. Where the clinical situation requires it, further tests are carried out to monitor changes in concentration over time.

Troponin is therefore part of an assessment process and does not replace the rest of the cardiological evaluation.

What you might feel during a blood test

The experience is similar to that of any blood test. You may feel the pressure of the tourniquet, the prick of the needle and a brief stinging sensation.

Afterwards, you may experience slight discomfort or a bruise may appear at the puncture site. If several tests are required, further blood samples may be taken or an existing intravenous line may be used.

Possible effects of venipuncture include local pain, bruising, slightly prolonged bleeding, dizziness and, less commonly, infection at the puncture site.

What does the 99th percentile for troponin mean?

Each troponin assay has its own upper reference limit, commonly referred to as the 99th percentile. Exceeding this limit indicates biochemical evidence of myocardial injury, but does not in itself determine whether the injury is acute or chronic, nor what its cause is. The value may vary depending on:

• Whether troponin I or T is measured.

• The manufacturer and the analyser.

• The units used.

• The reference population used.

• The possible use of sex-specific reference limits.

• The laboratory protocol.

For this reason, figures obtained using different methods should not be compared directly, nor should a single assumed normal value be used for all laboratories.

Causes of elevated troponin other than a coronary infarction

Elevated troponin indicates damage to the heart muscle, but this damage can result from various mechanisms. Cardiac causes include heart failure, myocarditis, certain arrhythmias, Takotsubo syndrome, some hypertensive crises, trauma and certain cardiac procedures.

It may also be elevated in systemic diseases affecting the heart, such as pulmonary embolism, sepsis, shock, hypoxaemia or severe anaemia.

In chronic kidney disease, there may be a persistent elevation. This should not be attributed solely to reduced troponin clearance, as structural heart disease and chronic myocardial damage may coexist.

Following certain prolonged or extreme physical exertions, transient elevations may occur in some individuals. This history should be reported, but it does not automatically allow the result to be attributed to exercise.

Type 1 myocardial infarction, type 2 myocardial infarction and non-ischaemic myocardial injury

Type 1 myocardial infarction is usually associated with the rupture or erosion of a plaque in a coronary artery and the formation of a thrombus. Type 2 myocardial infarction occurs when ischaemia results from an imbalance between the supply of oxygen and the heart muscle’s oxygen requirements, without acute coronary thrombosis being the primary mechanism.

It may occur, for example, during severe anaemia, hypoxaemia, hypotension or certain tachyarrhythmias. An elevated troponin level in these situations is not sufficient to diagnose a type 2 myocardial infarction; there must also be evidence of ischaemia.

When there is acute damage to the heart muscle without sufficient evidence of ischaemia, the condition is referred to as non-ischaemic myocardial injury.

Is it possible to have a heart attack with an initially low troponin level?

Yes, particularly when the first sample is taken shortly after the onset of symptoms. The concentration may not yet have risen, and it may be necessary to repeat the test.

Furthermore, an abnormal electrocardiogram or an unstable clinical condition requires intervention even if the initial troponin level is low. A non-elevated level also does not rule out other possible cardiac causes of the symptoms.

Therefore, the result must always be interpreted as part of the overall clinical assessment.

Limitations of troponin analysis

Troponin detects myocardial damage, but does not, on its own, identify the cause. It does not allow the coronary arteries to be visualised, the affected area to be pinpointed, the valves to be examined, or the heart’s pumping capacity to be measured directly.

A sample taken too early may not be conclusive. A chronic elevation may make interpretation difficult when there are no previous results to compare it with. Nor are the different troponin assays directly interchangeable.

In rare cases, a result that does not fit the clinical picture may be influenced by analytical interference. The laboratory may then re-test the sample or use other verification strategies.

Troponin, electrocardiogram and other cardiac tests

Troponin is usually interpreted alongside an electrocardiogram, which provides information on the heart’s electrical activity and may reveal abnormalities consistent with ischaemia or other heart problems.

Depending on the situation, repeat ECGs, echocardiography, coronary CT angiography, coronary angiography, cardiac MRI or other tests may be required. These investigations address different issues.

Troponin detects cell damage. The electrocardiogram assesses electrical activity. Echocardiography allows the structure, movement and function of the heart to be assessed, whilst coronary tests examine the arteries. The choice depends on the symptoms, clinical risk and suspected cause.

When to seek urgent care

In the event of persistent chest pain or tightness, severe shortness of breath, cold sweats, fainting, sudden deterioration or other symptoms that may indicate an acute heart problem, you should seek urgent medical attention.

You should not wait to have a troponin test carried out on an outpatient basis, nor should you rely on a previous result to rule out a current medical emergency on your own.

Specialists in cardiac assessment at the Publio Cordón Memorial Hospital

At Publio Cordón Memorial Hospital, cardiological assessment forms part of the Cardiology department, within the Cardiovascular Centre. The department is headed by Dr Felipe Hernández Hernández.

Cardiology is organised into the Clinical Cardiology Unit, the Electrophysiology and Arrhythmias Unit, the Haemodynamics and Interventional Cardiology Unit, and the Advanced Cardiac Imaging Unit, which work in a coordinated manner depending on the clinical situation.

The Haemodynamics and Interventional Cardiology Unit, also headed by Dr Felipe Hernández Hernández, specialises in coronary artery disease and its diagnosis and treatment using percutaneous procedures.

Troponin tests are processed in the clinical laboratory and the results are considered alongside the patient’s symptoms, electrocardiogram and the rest of the medical assessment.

Medical information for general guidance

This factsheet aims to help you understand what high-sensitivity cardiac troponin measures, why its levels may rise, why it is sometimes necessary to repeat the test, and how it forms part of the assessment of a possible heart muscle injury.

Memorial Publio Cordón Hospital promotes accurate, understandable and useful medical information, linked to specialist care, research, scientific dissemination and advances in medicine.

The interpretation of troponin levels depends on the method used by the laboratory, the time of blood collection, the symptoms, the electrocardiogram and the trend observed across multiple test results. A single test result should not be used to confirm or rule out a heart attack, nor to decide whether urgent care is required.