A hematocrit test is a type of blood test. Your blood is made up of red blood cells, white

blood cells, and platelets. These cells and platelets are suspended in a liquid called plasma. A

hematocrit test measures how much of your blood is made up of red blood cells. Red blood

cells contain a protein called hemoglobin that carries oxygen from your lungs to the rest of

your body. Hematocrit levels that are too high or too low can indicate a blood 

disorder, dehyfration, or other medical conditions.