Understanding Cardiac Biomarkers in Your Blood Test

Cardiac biomarkers are blood tests that look for specific proteins or other substances released when the heart is under stress or has been injured. They are among the most important tests in medicine because they help doctors quickly determine whether chest pain or other symptoms are coming from the heart and how serious the situation is.

If you have had cardiac biomarkers tested — usually in an emergency department, hospital, or cardiology clinic — this article will help you understand what each test measures, what your result means, and what may happen next.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What are cardiac biomarkers?

The heart is a muscle that works continuously, pumping blood to every part of the body. When the heart is healthy, very little of its specialized proteins escapes into the bloodstream. When heart muscle cells are injured — for example, when the blood supply to part of the heart is suddenly reduced during a heart attack — those proteins leak out and can be measured in a blood sample.

Other cardiac biomarkers respond to stretch and stress on the heart, rather than direct injury. When the heart is working too hard or struggling to pump effectively, it releases hormones that can be measured in the blood. These are useful for diagnosing and monitoring heart failure.

The most commonly used cardiac biomarkers fall into two main groups:

Markers of heart muscle injury — including troponin, creatine kinase, and CK-MB. These rise when heart cells are damaged.
Markers of heart strain — including BNP and NT-proBNP. These rise when the heart’s pumping chambers are stretched or stressed.

Your doctor will choose which biomarkers to order based on your symptoms. For someone with sudden chest pain, troponin is usually the most important test. For someone with shortness of breath that could be heart failure, BNP or NT-proBNP is usually most important.

Why are cardiac biomarkers tested?

Cardiac biomarkers are ordered in several common situations:

Chest pain. Troponin is the standard test for any patient with chest pain that may be coming from the heart. It is one of the first tests done in emergency departments around the world.
Other symptoms suggesting heart trouble. Shortness of breath, sudden severe fatigue, palpitations, lightheadedness, or pain in the jaw, neck, shoulder, or arm may all prompt cardiac biomarker testing, particularly in older adults or people with risk factors for heart disease.
To diagnose heart failure. BNP or NT-proBNP is often the first test used to determine whether shortness of breath is due to heart failure or another cause.
After a confirmed heart attack. Repeat biomarker tests track how the heart is recovering and whether the original injury is still ongoing.
To monitor heart failure. BNP or NT-proBNP can be repeated periodically to help assess whether heart failure is stable or worsening.
Before and after certain procedures. Cardiac biomarkers are sometimes measured before and after major surgery, cardiac procedures, or treatments that can affect the heart, such as some chemotherapy drugs.

How are the tests performed?

Cardiac biomarkers are measured on a small sample of blood drawn from a vein in the arm. No fasting or special preparation is needed. In emergency situations, results are often available within an hour. In some cases, the tests are repeated several hours after the first sample to look for changes — this is particularly important for troponin, because the pattern of rising or falling values is just as important as a single measurement.

Troponin

Troponin is the single most important cardiac biomarker for diagnosing a heart attack. It is a protein found inside heart muscle cells, and only very small amounts are normally present in the bloodstream. When heart cells are injured, troponin leaks into the bloodstream, and blood levels rise.

Modern hospitals use very sensitive troponin tests that can detect even tiny amounts of injury. These “high-sensitivity” troponin tests have dramatically improved how quickly heart attacks can be diagnosed or ruled out.

What troponin can tell you

Troponin levels are reported in nanograms per litre (ng/L) or nanograms per millilitre (ng/mL), depending on the laboratory. Reference ranges vary considerably between laboratories — some report troponin as detectable down to a single-digit value, while others use larger units. The specific number on your report will be compared to that laboratory’s normal cutoff.

What matters most is the pattern of troponin values over time:

Troponin below the laboratory cutoff that stays unchanged over several hours — strongly suggests that no significant heart muscle damage has occurred. In emergency departments, this pattern is often used to confirm that a patient is not having a heart attack.
Troponin above the cutoff that rises or falls significantly between measurements — usually indicates acute heart injury. In a patient with chest pain or other symptoms suggesting a heart attack, this rising or falling pattern is the key feature that confirms the diagnosis.
Troponin above the cutoff that stays at the same level over time — suggests that some heart muscle has been damaged in the past or that the heart is under chronic strain, but that there is no new acute injury. This pattern is sometimes seen in patients with severe kidney disease, advanced heart failure, or after a previous heart attack.

Other causes of an elevated troponin

While troponin elevations always mean heart muscle injury, not every elevation is caused by a heart attack. Other situations that can raise troponin include:

Severe heart failure
Myocarditis (inflammation of the heart muscle)
Pulmonary embolism (a blood clot in the lungs that puts strain on the heart)
Severe high blood pressure
Sepsis or severe infection
Severe chronic kidney disease (which slows the clearance of troponin from the blood)
Strenuous, prolonged exercise such as a marathon
Some chemotherapy drugs that can damage the heart
Cardiac procedures, including surgery and ablation

Your doctor will review the troponin pattern alongside your symptoms, ECG, and other findings to determine what is causing the elevation.

BNP and NT-proBNP

B-type natriuretic peptide (BNP) and N-terminal pro-BNP (NT-proBNP) are hormones released by the heart’s pumping chambers when they are stretched. The greater the strain on the heart, the more of these hormones are released.

BNP and NT-proBNP measure essentially the same thing, but the absolute numbers and reference ranges are very different — laboratories generally report one or the other.

BNP

A typical reference range for BNP in adults without heart failure is below 100 pg/mL. Higher values strongly suggest heart failure, with values above 400 pg/mL typically indicating moderate to severe disease.

NT-proBNP

NT-proBNP values are normally higher than BNP values because NT-proBNP stays in the bloodstream longer. Typical reference ranges vary considerably by age:

For adults under age 50, NT-proBNP below 450 pg/mL is generally considered normal.
For adults 50–75, the cutoff is typically below 900 pg/mL.
For adults over 75, the cutoff is typically below 1800 pg/mL.

Higher values increase the likelihood of heart failure.

What BNP or NT-proBNP can tell you

Very low values make heart failure unlikely. If a patient with shortness of breath has a normal BNP or NT-proBNP, the breathing problem is probably not coming from heart failure, and doctors will look for other causes such as lung disease.
Elevated values support a diagnosis of heart failure, particularly when symptoms and imaging tests also point in that direction.
Trends over time can help track whether heart failure is improving or getting worse. A falling BNP or NT-proBNP value in a patient being treated for heart failure usually indicates the treatment is working.

Other factors that affect BNP and NT-proBNP

Age. BNP and NT-proBNP rise naturally with age.
Kidney disease. Both markers are cleared by the kidneys, so impaired kidney function raises levels independently of heart failure.
Obesity. BNP and NT-proBNP tend to be lower in people with higher body weight, which can make the tests less sensitive for detecting heart failure.
Atrial fibrillation can raise both markers even in the absence of heart failure.
A medication called sacubitril/valsartan (used to treat heart failure) raises BNP levels but lowers NT-proBNP. If you are taking this medication, NT-proBNP is generally the more useful test.

Creatine kinase (CK) and CK-MB

Creatine kinase is an enzyme found in heart muscle, skeletal muscle, and the brain. There are several forms of CK, called isoenzymes. The form most specific to the heart is called CK-MB.

Before troponin testing became widely available, CK and CK-MB were the primary blood tests used to diagnose heart attacks. Today, troponin has largely replaced them because it is much more specific to heart muscle injury. However, CK and CK-MB are still measured in some specific situations:

When monitoring for additional heart muscle injury in a patient already known to have had a recent heart attack, CK-MB can sometimes detect a new event more clearly than troponin in the days immediately after a heart attack
When evaluating muscle injury, total CK rises significantly with muscle damage from any cause, including strenuous exercise, trauma, certain medications such as statins, and severe muscle conditions
In some research and specialty cardiology settings

Typical adult reference ranges are approximately:

Total CK: 30–200 U/L (varies considerably with sex, age, muscle mass, and activity level)
CK-MB: 3–5% of total CK

A high total CK with normal or only mildly elevated CK-MB usually points to skeletal muscle injury rather than heart muscle injury. A high CK-MB level rising in the right pattern over time can suggest heart muscle injury.

Other cardiac-related blood tests

Several other blood tests are sometimes considered “cardiac” tests, depending on the situation:

D-dimer. Used to help rule out pulmonary embolism (blood clot in the lung) and aortic dissection. A normal D-dimer makes these conditions unlikely. Discussed in more detail in our coagulation panel article.
Lipid panel. Total cholesterol, LDL, HDL, and triglycerides are not direct cardiac biomarkers, but they are central to estimating long-term cardiovascular risk. See our lipid panel article.
High-sensitivity C-reactive protein (hs-CRP). A measure of low-level inflammation that is sometimes used as one factor in estimating cardiovascular risk. Discussed in our inflammatory markers article.
Lipoprotein(a) — Lp(a). A specific type of cholesterol particle, partly inherited, that increases cardiovascular risk independently of LDL. Increasingly measured in patients with a strong family history of early heart disease.
Homocysteine. An amino acid that has been linked to cardiovascular risk, though the clinical role of this test is now considered limited.

What happens after cardiac biomarker testing?

The next steps depend heavily on the results and the reason the tests were done.

Troponin negative and stable in someone with chest pain: Heart attack is very unlikely. The doctor will look for other explanations for the symptoms, which may include acid reflux, muscle or chest wall pain, anxiety, lung problems, or other non-cardiac causes. Depending on overall risk, additional testing such as a stress test or imaging may still be recommended on an outpatient basis.
Troponin elevated in someone with chest pain or ECG changes: A heart attack is the most likely cause. Treatment may include medications to thin the blood and relax blood vessels, and often an urgent procedure called cardiac catheterization, in which a thin tube is threaded into the heart’s blood vessels to find and open any blockage.
Troponin elevated in someone without classic heart attack features: Other causes of heart muscle injury are considered, such as severe heart strain from another illness, myocarditis, or chronic conditions. Additional testing, such as an echocardiogram and cardiac MRI, may follow.
BNP or NT-proBNP normal in someone with shortness of breath: Heart failure is unlikely, and other causes such as lung disease, asthma, or anxiety are more likely.
BNP or NT-proBNP elevated: Heart failure is likely, and additional testing, such as an echocardiogram, is usually done to confirm the diagnosis and identify which type of heart failure is present.
Follow-up testing. Patients diagnosed with heart failure or recovering from a heart attack will usually have repeat testing along with cardiology follow-up. Many will be started on specific medications to protect the heart and prevent future events.

Questions to ask your doctor

Was my troponin level normal or elevated?
If my troponin was elevated, do you think I had a heart attack, or is something else causing it?
How does my result compare to the laboratory’s cutoff for normal?
Did my troponin change between the first and second blood draw?
If my BNP or NT-proBNP is elevated, do I have heart failure?
Will I need an echocardiogram, stress test, or cardiac catheterization?
Are there medications, recent activities, or other conditions that could be affecting my results?
What treatment do you recommend based on my results?
Should I be referred to a cardiologist?
What follow-up testing will I need over the coming weeks and months?