Blood Tests for Heart Disease

The most commonly performed test in patients with any problems with their health are blood tests, and this is true even in the case of heart diseases. You may be asked to come to the pathology lab having observed an overnight fast (i.e. no food or water intake from midnight till the test) as this will provide valuable information.

The most commonly performed blood tests are:

•    Complete blood count
•    Kidney function
•    Liver function
•    Fasting blood cholesterol
•    Fasting blood sugar
•    Thyroid function tests
•    Special blood tests

Your doctor will only request the tests that will help in diagnosis.

Complete blood count (CBC)

This test assesses the hemoglobin content of the blood and the white cell count. Hemoglobin is what makes the blood red, and carries oxygen. When this is low, it is called ‘anemia’. Anemia is a common cause of heart disease, and can be due to a number of factors such as poor diet, blood loss and hookworm infestation. It is easily treated with tablets, though sometimes a blood transfusion may be required. The white cells are cells in the blood that fight infection. There is no strong relation between white cell counts and heart disease, though a high white cell count may occur if there is infection or inflammation ongoing in the body or the heart.

Kidney function tests

This helps assess whether or not the kidneys are functioning normally. It assesses the sodium, potassium, urea and creatinine levels in the blood. When the kidney function is abnormal, it could be due to a number of causes, including poor blood supply to the kidney, dehydration, drugs and other treatment, or problems with the kidney itself. Kidney function tests are also useful to monitor treatment prescribed for heart problems, as many of these drugs are broken down in the kidneys and can be toxic to them.

Liver function tests

This assesses the function of the liver in getting rid of toxins and metabolising drugs. The liver is a vital organ that gets rid of a number of toxins in the blood. Its function can be affected by high intake of alcohol, certain drugs, viral inflammation (hepatitis) and sometimes by problems within the liver itself. By knowing what the liver function is, your doctor will be able to prescribe treatment that is good for the heart and does not affect the liver.

Fasting blood cholesterol

This provides the doctor with valuable information regarding how much fat there is in the blood. A high blood cholesterol is associated with thickening of the arteries (called atherosclerosis) and the development of heart attacks and strokes (for further information, please refer to our booklet ‘High Cholesterol, Lipids and Heart Disease’). Ideally this test is best done first thing in the morning on an empty stomach so as the get the true value. When elevated, your doctor will either give you dietary advice, prescribe drugs or both.

Fasting blood sugar

This test is done to see if the patient has diabetes. Diabetes mellitus is a condition where the production of insulin in the body is low, and thus the blood sugar level is high (for further information, please refer to our booklet ‘Diabetes and Heart Disease’). A number of research studies have shown a strong relationship between diabetes and heart disease. If this is elevated, patients are advised either dietary control, tablets, insulin injections or all of these.

In some patients, a test called the postprandial blood sugar test may be performed. This test helps evaluate the body’s response to ingestion of food and the release of insulin. A high postprandial blood sugar above the normal range points towards a diagnosis of diabetes mellitus.

Thyroid function tests

This test assesses the function of the thyroid gland, which is a small gland in front of the throat. It secretes hormones that perform a number of functions. By testing this, it is possible to assess whether the gland is functioning normally or whether it is over-active or under-active. An overactive or under-active thyroid gland can cause heart problems such as palpitations and breathlessness.

Special blood tests

On occasions, the doctor may ask for special tests to assess other factors that can play a role in heart disease or even help diagnose heart disease. The list is long and has not been discussed here, but will be discussed with you by your doctor if required. Some of the tests include vitamin D levels, vitamin B12 levels and blood iron levels.