Enzymes are proteins that speed up chemical reactions and biological processes around the body. When your heart sustains damage or injury, it releases cardiac enzymes — also known as cardiac biomarkers — that doctors can test to measure the health impact of a suspected heart attack.
Over the years, healthcare professionals have used different cardiac enzymes to monitor damage.
At present, they test for cardiac troponins. The proteins troponin T and troponin I are the key biomarkers in a cardiac enzyme test. Skeletal muscle also produces troponins, but different subtypes. This means that if troponins I and T show up in a cardiac enzyme test, they’re more likely to highlight cardiac problems.
This biomarker helps let your doctor know when your heart has been under stress. It can also reveal if your heart muscle isn’t getting enough oxygen.
If your doctor suspects that you’re having a heart attack or that you may have had one recently or have other damage to the heart due to inflammation (myocarditis), they may recommend a cardiac enzyme test. This test measures the level of certain proteins circulating in your bloodstream. Such a test allows the doctor to confirm your diagnosis and start treatment ASAP.
After a heart attack, levels of troponins T and I may start to increase within around 4 hours. They’ll stay high for several days, meaning that they’re useful for indicating a heart attack.
A cardiac enzyme test doesn’t require any preparation. You don’t have to fast or stop taking certain medications.
In many cases, a doctor measures cardiac enzymes in an emergency situation when they suspect a heart attack. You or someone close to you should tell your doctor about any medications and supplements you take.
What your doctor may ask
Your doctor should also know any other important medical information, including:
- any previous heart disease or stroke history
- whether you have high blood pressure
- any recent surgeries or other procedures
- how long symptoms have been occurring
- whether you have kidney problems
A blood test for cardiac enzymes is similar to a standard blood test. The healthcare professional inserts a needle into your arm and draws enough blood to fill a small vial or two. You might feel a little pain during the insertion of the needle.
Your doctor will assess your biomarker levels to confirm whether you’ve had a heart attack and assess the extent of damage to the heart muscle. They’ll often check levels more than once to see if they change over time.
As well as checking your biomarkers, your doctor may also want to test your blood for other markers that give information about your heart and health status.
This includes your:
- cholesterol levels
- blood glucose (sugar) levels
- white and red blood cell count, as well as your platelet levels
- your levels of electrolytes, such as sodium and potassium
- your kidney function
- levels of B-type natriuretic peptide (BNP), a hormone that can indicate heart failure
A cardiac enzyme test is relatively simple and painless. You may have some minor bruising or temporary soreness at the site where the needle is inserted to draw blood.
Be sure to tell the person drawing your blood if you have an allergy to latex. This can help you avoid complications. Otherwise, the test is safe and mostly risk-free.
Test results of your cardiac enzymes can indicate whether it’s likely you had a heart attack or incurred other types of heart damage.
For example, most healthy young people have no increased troponin T circulating in their bloodstream. The more damage the heart muscle incurs, the higher the levels of troponin T circulating in your blood will be. Doctors now use high-sensitivity troponin to rule out damage with high sensitivity.
Cardiac troponin T is measured in in nanograms per milliliter (ng/mL). If your troponin T level is above the 99th percentile for the test, your doctor will likely diagnose a heart attack.
Levels that start high and fall suggest a recent injury to the heart. It could have been a mild heart attack or heart muscle damage. You may not have even been aware of it.
Cardiac enzyme test results are usually available within an hour of collecting the blood sample.
Cardiac enzyme levels can rise for reasons other than a heart attack. For example, sepsis, a type of blood infection, can lead to elevated troponin levels. The same is true for atrial fibrillation, a common heart rhythm problem.
Other factors that could affect your test results include:
- a blood clot in the lungs
- acute or chronic heart failure
- brain injury
- cardiac contusion due to a chest wall injury
- cardioversion to treat atrial fibrillation or atrial flutter
- chemotherapy treatments
- coronary angioplasty
- defibrillation for ventricular fibrillation or tachycardia
- end-stage kidney disease
- myocarditis or myopericarditis
- open heart surgery
- other heart conditions, such as cardiomyopathy
- radiofrequency catheter ablation of arrhythmia
- strenuous exercise
- valvular heart disease
Because other factors can trigger a spike in cardiac enzyme levels, your doctor won’t rely solely on your enzyme levels alone to diagnose a heart attack.
They will also use an electrocardiogram and symptoms to confirm a diagnosis.
If your doctor diagnoses a heart attack, it’s vital that you follow their advice about medications, diet, exercise, and other healthy lifestyle choices. They may also recommend cardiac rehabilitation.
If you have high cardiac enzyme levels but haven’t had a heart attack, your doctor will talk to you about ways to keep your heart healthy.
This can help prevent a future heart attack.