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What Are Blood Tests?

By taking and testing a small sample of a person’s blood, doctors can check for many kinds of diseases and conditions. Blood tests help doctors check how the body’s organs — such as the kidneys, liver, thyroid, and heart — are working, and see if medical treatments are helpful. 

Most blood tests take only a few minutes. They’re done at some doctor’s offices, and at community labs, diagnostic centers, and hospitals. A doctor, nurse, or phlebotomist (fleh-BOT-eh-mist, someone who is trained to take blood samples) will take the blood sample. Sometimes the sample is tested on-site; other times it will go to a lab.

Blood test results can be ready in a few hours or take a few days, depending on the test and whether the sample was sent to a lab.

What Are the Types of Blood Tests?

Some of the blood tests most often done are:

Medically reviewed by: Larissa Hirsch, MD
Date reviewed: September 2021