Blood tests can be used to evaluate heart disease. Your blood sample may be tested for one or more of the following:
- Cholesterol. A full test includes measuring total cholesterol, high-density lipoprotein (HDL) cholesterol (the good kind), low-density lipoprotein (LDL) cholesterol (the bad one) and triglyceride levels. These results allow your doctor to calculate the ratio of LDL to HDL. Blood levels of triglycerides vary according to food intake. It's best to not eat or drink (other than water) for at least 8 hours before the blood is drawn.
- Cardiac enzymes. After a heart attack, enzymes from damaged heart cells may leak into blood. If you experience chest pain, your doctor may test your blood for these enzymes. Specific enzymes include CK (creatine kinase), CK-MB (the form of creatine kinase found in heart muscle), and cardiac troponin I or T.
- C-reactive protein (CRP). A high C-reactive protein suggests the presence of inflammation in the body. Because atherosclerosis is associated with inflammation in your body’s arteries, C reactive protein tends to go up in people with more atherosclerosis. Other diseases that cause inflammation, like arthritis, can also make it rise.
- B-type natriuretic peptide (BNP). This test detects a chemical released by the heart when it is under strain. BNP can help separate shortness of breath due to heart failure from shortness of breath caused by lung disease. Higher BNP levels mean a higher risk of heart complications.
- Oxygen content. Measurement of blood oxygen helps to determine whether your overall circulation is sufficient, whether the lungs are providing enough oxygen to the bloodstream and/or whether there is evidence of poor blood flow from the heart to the lungs. Your oxygen level can be most easily measured with a device placed on a finger (called a pulse oximeter). But it is more accurately measured using blood drawn from an artery. Standard blood tests use blood from a vein, usually drawn at the bend of the elbow.
- Prothrombin time. One of the blood tests that reflect how quickly blood will clot. Medications that slow blood clotting include anticoagulants, such as warfarin (Coumadin), and antiplatelet drugs, such as aspirin. Although anti-coagulants are referred to as blood thinners, they don't actually "thin" the blood. Instead they alter proteins in the blood that are responsible for clotting. Antiplatelet agents act differently. They prevent platelets from clumping and forming clots. People that take warfarin need to have periodic prothrombin time blood tests to make sure the dose is effective, yet safe (too high a dose can cause bleeding). Prothrombin time is not measured in people taking antiplatelet agents.
- Thyroid disease. Doctors often use blood tests to check for thyroid disease because an overactive thyroid gland can lead to a racing heartbeat and an underactive gland can cause a high blood cholesterol level.