Your blood is living tissue made up of liquid and solids. The liquid part, called plasma, is made of water, salts, and protein. Over half of your blood is plasma. The solid part of your blood contains red blood cells, white blood cells, and platelets.
Red blood cells (RBC) deliver oxygen from your lungs to your tissues and organs. White blood cells (WBC) fight infection and are part of your body's defense system. Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones. Red blood cells live about 120 days, and platelets live about 6 days. Some white blood cells live less than a day, but others live much longer.
Blood tests show whether the levels of substances in your blood are within a normal range. They help doctors check for certain diseases and conditions. They also help check the function of your organs and show how well treatments are working. Some of the most common blood tests are blood count tests, which measure the number, size, and shape of cells and platelets in the blood.
- Blood and Diversity (American Red Cross)
- Blood Types (American Red Cross)
- ClinicalTrials.gov: Blood Cells (National Institutes of Health)