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Blood tests for cardiac assessment

A common diagnostic tool used to measure cardiac enzymes, oxygen levels, clotting time, and lipid levels.

Most of us have had blood tests at some point in our lives. It's a very common way for doctors to diagnose a wide variety of conditions or to look for indications that further investigation is necessary. If you have heart disease, you likely have blood samples taken as part of your ongoing care.

What do blood tests tell us?

These tests are used to assess your cholesterol and triglyceride levels. Other reasons can include assessing cardiac enzymes, oxygen content, and clotting time.


The lipid blood test measures your your HDL and LDL levels, total cholesterol, and the ratio, plus your triglyeride levels. Usually this test is done in the morning after fasting for 12 hours. This blood test is important in determining if your cholesterol can be controlled through diet and exercise or if medication is required. If you are taking medication, the test will monitor if it is achieving the desired results. If not, an adjustment in type or dose of medication may be required.

Cardiac enzymes

If you are having chest pains, your doctor will look for cardiac enzymes and proteins in your blood. Their presence indicates damage to your heart has occurred, such as from a heart attack.

If you go to emergency at the hospital with signs or symptoms associated with heart attack or heart disease they will most likely do a blood test for the presence of cardiac enzymes. These enzymes don't always appear immediately - it may take several hours - but they can also remain in your blood for several days after a heart event.

If you have had a heart attack, doctors may monitor your enzymes for a few days to determine if the levels are subsiding as expected - or increasing, which could indicate further damage.

According to the Mayo Clinic Heart Book, there are some occasions when cardiac enzymes are elevated falsely. This can occur in "marathon runners, athletes with muscle injuries, people with chronic kidney insufficiencies, and individuals with a genetic predisposition for elevated levels of certain enzymes."

Oxygen levels

Your oxygen levels indicate if enough oxygen is circulating in your bloodstream. Blood that is returning to the heart is taken from a vein. If your doctor wants to assess your oxygen levels just after the blood passes through the lungs, the test will be done using an artery. Oxygen levels can also be analyzed with a device which is placed on your finger. It measures the oxygen in your blood by using a special light to assess the redness of your blood. Typically, this device, which looks a bit like a clothes pin or a finger splint, is used when you have an angiogram or angioplasty, or during monitoring in emergency or an intensive or cardiac care unit.

Clotting time

If you are taking anticoagulants (commonly known as blood thinners), there's a balance to be achieved between preventing abnormal clotting and avoiding a dangerous lack of clotting or excessive bruising. Warfarin, in particular, has different results in different people, so if you are on Warfarin, or if there are concerns about your clotting time, your doctor will want to test your clotting periodically.

What to expect

Many people feel nervous about having their blood taken. I can relate because I don't handle the sight of blood very well, so I always look the other way when I have my blood taken. Others are nervous about needles. But, fortunately it's a fast and relatively painless procedure. For some tests, all that's required is a few drops from the finger tip. In other cases they will put a rubber band around your arm to make your vein bulge then insert a needle to which they can attach a vial or vials to collect the sample. You may feel the pin prick and a bit of a stinging sensation but that's about it.

If you are on blood thinners, you may have to apply some pressure on the tiny puncture hole for a minute or two to stop bleeding and you may experience some bruising. You will be given a bandaid to cover the puncture.

Honestly, the worst part is having to fast overnight, (I love my breakfast and morning coffee!) which is sometimes required - especially for lipid (cholesterol and triglyceride) levels.


The only risk related to having blood taken is slight bruising where the needle went in. The risk of infection or contamination is inconsequential if conditions are sanitary and needles are sterile.

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