What are blood tests?

Blood tests are used to measure or look at cells, chemicals, proteins, or other substances in your blood. Blood testing, also known as blood work, is one of the most common types of lab tests. Blood work is often included as part of a regular checkup. Blood tests are also used to:

• Help diagnose certain diseases and conditions.
• Monitor a chronic (long-lasting) disease or condition, such as diabetes or high cholesterol.
• Find out if treatment for a disease is working.
• Check how well your organs are working. Your organs include your liver, kidneys, heart, and thyroid.
• Help diagnose bleeding or clotting disorders.
• Find out if your immune system is having trouble fighting infections.

What are the different types of blood tests?

There are many different types of blood tests. Common ones include:

• Complete blood count (CBC). This test measures different parts of your blood, including red and white blood cells, platelets, and hemoglobin. A CBC is often included as part of a regular checkup.
• Basic metabolic panel (BMP). This group of tests measures certain chemicals in your blood, including glucose, calcium, and electrolytes.
• Blood enzyme tests. An enzyme is a protein that speeds up certain chemical reactions in your body. There are many types of blood enzyme tests. Some of the most common types are troponin and creatine kinase tests. These tests are used to find out if you've had a heart attack and/or if your heart muscle is damaged.
• Blood tests to check for heart disease. These include cholesterol tests and a triglyceride test.
• Blood clotting tests, also known as a coagulation panel. These tests can show if you have a disorder that causes too much bleeding or too much clotting.

What happens during a blood test?

A health care provider will need to take a sample of your blood. This is also called a blood draw. When a blood draw is taken from a vein, it's known as venipuncture.

During venipuncture, a lab professional, known as a phlebotomist, will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Venipuncture is the most common way to do a blood test.

Other ways to do a blood test are:

• A finger prick test. This test is done by pricking your fingertip to obtain a small amount of blood. Finger prick testing is often used for at-home test kits and rapid tests. Rapid tests are easy to use, provide fast results, and require little or no special equipment.
• A heel stick test. This is most often done on newborns. During a heel stick test, a provider will clean your baby's heel with alcohol and poke the heel with a small needle. The provider will collect a few drops of blood and put a bandage on the site.
• Arterial blood test. This test measures your oxygen levels. Blood from arteries has higher levels of oxygen than blood from a vein. So, for this test, blood is taken from an artery instead of a vein. Blood may be taken from your wrist, arm, or groin area. It is often drawn by a specially trained provider. You may feel a sharp pain when the provider inserts the needle into the artery to get the blood sample.

Will I need to do anything to prepare for the test?

You don't need any special preparations for most blood tests. For some tests, you may need to fast (not eat or drink) for several hours before your test.

You may need to stop taking certain medicines before your test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to having a finger prick test or venipuncture. During venipuncture, you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

There is very little risk to your baby with a heel stick test. Your baby may feel a little pinch when the heel is poked, and a small bruise may form at the site.

Collecting blood from an artery is more painful than collecting from a vein, but complications are rare. You may have some bleeding, bruising, or soreness at the spot where the needle was put in. Also, you should avoid lifting heavy objects for 24 hours after the test.

Is there anything else I should know about blood testing?

Blood testing can provide important information about your health. But it doesn't always give enough information about your condition. If you've had blood work, you may also need other types of tests before your provider can make a diagnosis.

To understand the results of your blood test, your provider may consider your symptoms, medical history, and the results of other tests.

Learn more about laboratory tests, reference ranges, and understanding results.