Blood Tests: What It Is and What to Expect
Medically reviewed by Sumiran Racherla, MD, Internal Medicine. Last reviewed: October 23, 2026.
What kind of doctor provides Blood Tests?
Your primary care doctor or a specialist, a doctor trained in one area of medicine, can order a blood test. A phlebotomist, a lab professional who draws blood, usually takes the sample. A direct primary care or concierge doctor can be a first stop for an evaluation and can refer you to a specialist when needed.
What it is
Blood tests measure or look at cells, chemicals, proteins, or other substances in your blood. Blood testing is also called blood work. Here, blood tests means blood testing in general, not any one specific test.
A complete blood count, or CBC, measures red and white blood cells, platelets, and hemoglobin. A basic metabolic panel measures chemicals in your blood, including glucose, calcium, and electrolytes. A lipoprotein panel measures LDL and HDL cholesterol and triglycerides, a type of fat in your blood.
Why a doctor might recommend it
Doctors use blood tests for several reasons.
- To help diagnose certain diseases and conditions
- To check on a long-lasting disease such as diabetes or high cholesterol
- To find out if a treatment is working
- To check how well your liver, kidneys, heart, and thyroid are working
How to prepare
You do not need any special preparation for most blood tests. For some tests, you may need to fast, which means not eating or drinking for several hours. Most people need to fast for 9 to 12 hours before a lipoprotein panel. Tell your provider about everything you take, because you may need to stop certain medicines before your test. Do not stop any medicine unless your provider tells you to. Follow your doctor's instructions about fasting and medicines.
What happens during it
Most blood tests use a draw from a vein, which is called venipuncture. The phlebotomist takes a blood sample from a vein in your arm using a small needle. A soft strap may be put around your arm first to make taking blood easier. The blood goes into a small tube, which is sent to a lab for testing. This usually takes less than five minutes.
A finger prick test uses a small amount of blood from your fingertip and is often used for at-home test kits and rapid tests. An arterial blood test takes blood from an artery to measure your oxygen levels.
Recovery
After the test, you will usually get some cotton wool or a plaster to cover the spot where the blood was taken. You may get some bruising or swelling there, but it should go away after a few days. After an arterial blood test, you should avoid lifting heavy objects for 24 hours. You may get your results after a few days, and usually within a few weeks.
Risks and side effects
There is very little risk to having a finger prick test or a blood draw from a vein. You may have slight pain or bruising where the needle went in, but most symptoms go away quickly. Taking blood from an artery is more painful than taking it from a vein, but problems are rare. You may have some bleeding, bruising, or soreness at that spot.
A bone marrow test, which is listed with blood tests, checks whether your bone marrow is healthy and making normal amounts of blood cells. It uses a larger needle to collect bone marrow, so it is not an ordinary blood draw. After a bone marrow test, call your provider if you are in serious pain or have fever, redness, swelling, or discharge at the needle site.
Who performs it
A phlebotomist, a lab professional, usually does a blood draw from a vein. Arterial blood is often drawn by a specially trained provider.
Common questions
Do I need to fast for a blood test?
You do not need to fast for most blood tests. Some tests do require fasting, which means no food or drink for several hours. Most people need to fast for 9 to 12 hours before a lipoprotein panel.
How long does a blood draw take?
A blood draw from a vein usually takes less than five minutes.
When will I get my blood test results?
You may get your results after a few days, and usually within a few weeks.
How does a direct primary care or concierge doctor fit in?
A direct primary care doctor charges a flat monthly fee instead of billing insurance, while a concierge doctor usually charges more and often works alongside insurance. Whichever doctor orders your test should talk to you about your results and explain what happens next.
Sources
- MedlinePlus - What You Need to Know About Blood Testing
- National Heart, Lung, and Blood Institute - Blood Tests
- NHS - Blood tests
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
