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Why Does My Doctor Need to Draw My Blood?

When you visit your healthcare provider, you provide a lot of information verbally or in writing—your family health history, medications you take and symptoms you experience. A physical exam reveals more information. But to get the complete picture of your health, your provider will typically need data that can only come from inside your body. That’s why you might be asked to roll up your sleeve and provide a blood sample.

“Blood work is necessary in lots of situations,” says UNC Health family medicine doctor Amber Komorian, MD. “It helps us assess your risk of certain conditions, or we can use it to identify the causes of your symptoms. It’s important monitoring for people managing chronic disease, because we can see how well-controlled that diagnosed condition is or assess side effects from medications you may be taking.”

Here’s what to know about the most common blood tests.

Types of Blood Tests

Here are some of the common tests your provider might order:

If you’re experiencing symptoms, your provider may order a more detailed test to look at a specific chemical or hormone in your blood.

Talking to Your Doctor About Which Tests You Need

Not everyone needs the same blood tests. In fact, you may not need any blood work as a young adult if you don’t have a family history of chronic disease.

“For young people without any health risks, who aren’t on any meds, who are asymptomatic, routine labs are unlikely to reveal new disease and aren’t as necessary,” Dr. Komorian says. “Once you’re past the age of 35, or have a family history of disease, it’s going to be more standard.”

Your provider can help you determine what tests you need based on your age, health history, symptoms, and risk factors, such as obesity or smoking.

“If you have specific symptoms or concerns, mention those, because we might do more testing if you’ve experienced weight gain and have a family history of certain conditions, for example,” Dr. Komorian says. “Your full history—symptoms, family history, medications—is guiding the decision.”

Understanding Blood Tests Results

After your blood is drawn, it’s sent to a lab to be tested. Your doctor receives the results and will explain them to you, but you may be able to see the results in your patient portal before your provider has had a chance to review.

“I definitely encourage people to reach out to their physician before going to Google to see what their results mean,” Dr. Komorian says. “Google doesn’t know the context for why those labs were ordered. Something may be marked red and look scary in the written report, but it might not be clinically significant or relevant for your case.”

For example, Dr. Komorian says it’s possible for one of your blood cell counts to be outside the normal range in a CBC test, but if you’re not having symptoms of anemia, it’s not a problem.

If something is outside a normal range, your provider will determine next steps, which may include an immediate follow-up or just watching and waiting over a period of years.

“Depending on whether it’s a small or large abnormality, we might do follow-up tests to confirm that finding,” Dr. Komorian says. “We don’t typically make huge decisions based on a small abnormality. We want to make sure it’s clinically relevant—that it’s associated with symptoms you’re having or a medication you’re taking.”

Preparing for Blood Work

Some blood tests can be done without any preparation, but for some tests, it will be recommended that you not eat or drink in the eight to 12 hours before your blood is drawn.

“For tests of cholesterol or diabetes, you can have abnormalities based on eating a meal, which is why fasting is recommended,” Dr. Komorian says. “Glucose shoots up after a meal, because your body is using energy from that meal; your levels when you haven’t eaten a meal are more relevant.”

If you’ve avoided blood tests because of a fear of needles, share that information with your provider.

“Our staff are great at distracting you,” Dr. Komorian says. “There are measures they can use, including desensitization. They’ll use a stimulus, such as something cold, to trick your mind into feeling that rather than the needle. They can play music to help. This affects lots of people, so people who draw blood are strong in this area.”


Questions about the lab work you may need? Talk to your doctor. If you need a doctor, find one near you.

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