Blood enzyme tests

Enzymes are chemicals which help to regulate a number of chemical reactions, and that take place in the body. Blood enzyme tests can be used to measure the levels and activity of certain enzymes. Some blood enzyme tests assess the liver enzymes and others test for damage to the heart. There are three main blood enzyme tests, which are used to check if an individual has had a heart attack or has experienced damage to their muscles; these are:

Creatine kinase

Creatine kinase is an enzyme which is produced by the majority of muscle cells. Creatine kinase is found in the brain, heart and the skeletal muscle cells; it helps the body to manufacture the energy needed to move. There are three forms of creatine kinase; these are:

CK-MB: this is mostly found in the heart muscle cells

CK-BB: this is mostly found in the brain

CK-MM: this is mostly found in the heart and skeletal muscles

Why would I need the test?

The creatine kinase test is usually recommended for people who have had chest pain or weakness in the muscles. The CK test is used to establish whether or not an individual has had a heart attack.

How is the test performed?

The test is done by collecting a sample of blood from the arm; a needle is inserted into a vein in the arm (usually on the inside of the elbow or the wrist) and a sample is collected in a syringe. Once the sample has been collected, it will be bottled, labelled and sent to the laboratory for analysis.

What do the results mean?

Levels of creatine kinase are higher if the heart muscle or other muscles in the body have been damaged; the levels of CK in the blood start to increase around 3-5 hours after a heart attack and levels usually peak after 18 hours. If your doctor suspects that you have had a heart attack, they may advise you to have a troponin test or a CK-MB test (levels of this form of CK are particularly high if the individual has had a heart attack).

People who have high muscle mass often have higher levels of creatine kinase, so those who regularly exercise and take part in intensive sporting activities will generally have much higher levels of CK than those who do less exercise.

High CK levels may also indicate muscle damage caused by accidents, sporting injuries or surgery.

Higher levels may also indicate problems with the thyroid gland.


Troponin is a protein that helps the muscles to contract. Troponin is found in the cardiac and skeletal muscle cells. There are three types of troponin; these are:

Troponin C (TnC)

Troponin T (TnT)

Troponin I (TnI)

Why would I need the test?

Your doctor may advise you to have a troponin test if you have experienced chest or muscle pain or if they suspect that you have had a heart attack. The troponin test is usually preferred to the CK test for those who are suspected of having a heart attack; this is because the test is more specific in terms of assessing damage to the heart muscle. In most cases, the troponin test is used in emergency departments, when patients have been admitted with chest pain and muscle weakness.

How is the test performed?

The test is performed by collecting a sample of blood from the arm; a needle is inserted into a vein in the arm and the blood is collected in a syringe. The sample is then put in a bottle, labelled and sent to the laboratory.

What do the results mean?

The forms of troponin found in the heart, TnI and TnT are not usually present in the bloodstream; however, following damage to the muscles, they are released into the blood. Levels of troponin and not usually high enough to be measured; this means that even a slight rise in the levels can signify damage to the cardiac or skeletal muscles.

Unlike the CK test, the levels of troponin are not usually affected by damage to other muscles; this means having surgery or having an accident or an injection will not affect the test results.

Enzyme-linked immunosorbent assay (ELISA)

What is the test used for?

The enzyme-linked immunosorbant assay (commonly known as the ELISA test) is used to test for infections or allergies. The test is used to detect the presence of antibodies and antigens in a sample of blood.

How does the test work?

The body produces a number of specific antibodies to combat specific types of bacteria or viral infections; if you have an infection, the immune system will make an antibody to fight off that particular infection so that you will be able to fend off illnesses and infections in the future. The blood sample shows which antibodies have been released into the bloodstream and therefore which infection or allergy has affected the body.

When is the test used?

The ELISA test is used for people with allergies, for example nut allergies (the test can be used to assess particular types of allergy, for example a peanut allergy) and specific types of infection, such as HIV (the virus which causes AIDS) and Lyme disease. This test is usually the first test used to assess whether or not an individual has contracted HIV; if the antibody to HIV is detected in the blood sample, this will probably mean the individual has HIV (the test is very accurate but positive results are almost always repeated to ensure the diagnosis is correct; negative results are very rarely repeated because the chances of a false negative are extremely low).

What do the results mean?

If the ELISA test is positive this means that specific antibodies are present in the blood; for example, if antibodies to HIV are found in the blood, this will indicate that an individual has HIV. In some cases, further tests may be required to confirm the diagnosis.

Blood Test Types

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