A blood test is when a sample of blood is taken from the body to be tested in a lab. Doctors order blood tests to check things such as the levels of glucose, hemoglobin, or white blood cells. This can help them detect problems like a disease or medical condition. Sometimes, blood tests can help them see how well an organ (such as the liver or kidneys) is working.
A complete blood count (CBC) test is a blood test that helps doctors check the level of different types of cells in the blood. A CBC measures:
red blood cells, which deliver oxygen to the different parts of the body
white blood cells, which help fight infections
platelets, which help blood clot to stop bleeding