Heart Attack Tests

CKMB

What is CK and CKMB?

Creatine kinase (CK) is an enzyme a protein that helps cells perform their normal functions—found in the heart, brain, muscle and blood of healthy people. Blood levels of CK rise when your muscle or heart cells are injured. CKMB is a form of the enzyme that is found mainly in heart muscle. While a high level of total CK can indicate damage to muscle, a high CKMB level suggests that there is disease or damage to the heart muscle specifically.

CKMB levels begin to rise within the first 4 to 6 hours after heart attack symptoms begin and reach their highest level after about 18 to 24 hours. Levels return to normal in about 2 or 3 days.

Who might have a CKMB test?

A CKMB test helps diagnose a heart attack. It is usually given to people experiencing chest pain or weakness immediately after a suspected heart attack and several times in the hours afterward. CK and CKMB levels can also be used to tell whether heart attack treatments such as clot-busting drugs are working.

What does the CKMB test entail?

A blood sample will be taken from a vein in your arm. In some hospitals, a bedside or point-of-care test is available that requires only a finger prick and a few drops of blood. The blood is placed on a strip and positive results are available almost immediately if the CKMB is present in an elevated amount. It takes about 15 minutes to ensure a negative result. The test takes less than a minute.

What do the results of a CKMB test mean?

A high level of CKMB, or an increase in the level between the first and subsequent tests, indicates that there has been some damage to the heart. Because CK can be found in muscles outside of the heart, the ratio of CKMB to total CK is more useful. If the CKMB level is more than 2.5% to 3% of the total CK, the heart muscle is most likely damaged.

What are the limitations of the CKMB test?

CKMB may not be detectable in the blood for three to six hours after the onset of heart attack symptoms; therefore, it is not useful in the very early diagnosis of a heart attack. African Americans and people with a muscular or athletic build have naturally higher CK levels and may have false positive tests (i.e., the test detects a problem when in reality there is none). Strenuous exercise, some medications, or drinking too much alcohol can increase CK levels. Patients with kidney failure may have high CKMB levels without having had a heart attack. In rare cases, chronic muscle disease, low thyroid hormone levels, and alcohol abuse can raise CKMB levels to those seen during a heart attack.

Myoglobin

What is myoglobin?

Myoglobin is a protein found in heart muscle and other muscles in the body. When the muscle is injured, myoglobin is released into the blood. Myoglobin levels rise about one to four hours after heart attack symptoms begin and reach their highest level eight to 12 hours later. Because myoglobin is released into the blood more rapidly than CKMB or troponin, it is useful for diagnosing a heart attack in the very early stages. Myoglobin levels fall off after about 24 hours.

Who might have the test?

Myoglobin tests help diagnose or rule out heart attack. The test is usually ordered in patients with chest pain who may be having a heart attack; levels will be checked every two to three hours from the time they enter the emergency room.

What does the test entail?

A blood sample is taken from a vein in your arm. In some hospitals, a bedside or point-of-care test is available that requires only a finger prick and a few drops of blood. The blood is placed on a strip and positive results are available almost immediately if myoglobin is present in an elevated amount. It takes about 15 minutes to ensure a negative result. The test takes less than a minute.

What do the results mean?

A high level of myoglobin, or an increase in the level between the first and subsequent tests, indicates that there has been very recent injury to the heart or other muscle tissue.

What are the limitations of this test?

High myoglobin levels indicate muscle damage but they can’t tell whether the heart specifically is affected. Other tests (CKMB or troponin) are needed to confirm that the heart is affected. Myoglobin levels can rise after muscle injections or strenuous exercise. Patients with kidney failure may also have higher myoglobin levels without having a heart attack. In rare cases, alcohol abuse and certain drugs can increase myoglobin levels.

Troponins

What are troponins?

Troponins are proteins found in skeletal and heart muscle fibers that help muscles to contract. Cardiac troponin tests measure levels of troponin T and troponin I because these are found only in heart muscle. When a person has a heart attack, troponin is released into the blood three to six hours later. The cardiac troponin test is better for diagnosing a heart attack than the CK, CKMB, or myoglobin tests because troponins are not found in the blood of healthy people. Damage to other muscles does not affect levels of the cardiac troponins. Troponin levels rise three to six hours after heart attack symptoms begin and stay high for up to one to two weeks after a heart attack.

Who might have the test?

Cardiac troponin tests help diagnose or rule out heart attack. Troponin tests are used in patients who have chest pain or other heart attack symptoms to see if they have had a heart attack or other heart damage. If you are hospitalized because of heart attack symptoms, you will be tested two to three times during a 12- to 16-hour period.

What does the test entail?

A blood sample is taken from a vein in your arm. In some hospitals, a bedside or point-of-care test is available in which only a finger prick and a few drops of blood are necessary. The blood is placed on a strip and positive results are available almost immediately if troponin levels are elevated. It takes about 15 minutes to ensure a negative result. The test takes less than a minute.

What do the results mean?

Troponins are not usually found in the blood of healthy people, so even slight elevations indicate some damage to the heart—usually a heart attack. Because troponin levels remain high for up to two weeks, a positive test may not distinguish between an ongoing heart attack or one you had earlier. A CKMB test can help in this situation.

What are the limitations of this test?

Troponins may not be detectable in the blood for three to 12 hours after the onset of heart attack symptoms; therefore, this test is not useful in the very early diagnosis of a heart attack. Patients with kidney failure may have higher troponin levels. Patients treated with heparin, a blood thinning medication, may get a falsely high troponin level with some test methods.

BNP

What is BNP?

B-type natriuretic peptides (BNP) or N-terminal proBNP (NT-BNP) are proteins that are released into the bloodstream when the heart does not work properly. They are relatively new markers that are used for diagnosing or ruling out heart failure.

Who might have the test?

BNP tests are useful for diagnosing or ruling out heart failure in patients with shortness of breath. Ongoing research also suggests that BNP testing may predict your risk of future heart problems, but it is not widely used for this purpose.

What does the test entail?

A blood sample is taken from a vein in your arm. In some hospitals, a bedside or point-of-care test is available that requires only a finger prick and a few drops of blood. The blood is placed on a strip and positive results are available almost immediately if BNP is present in an elevated amount. It takes about 15 minutes to ensure a negative result. The test takes less than a minute.

What do the results mean?

Levels of 100 picograms per ml (pg/ml) or higher are a sign of heart failure. BNP tests are also used to assess the effectiveness of heart failure therapy. Higher BNP levels may mean you have a higher risk for future heart problems.

What are the limitations of this test?

BNP levels fall in most patients taking heart failure medications, such as ACE inhibitors, beta blockers, and diuretics. The BNP test is relatively new and is not as widely available as the other blood tests (CKMB, troponin, myoglobin).

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