Blood is made up of red blood cells, white blood cells and platelets, suspended in plasma. Together, those comprise about 45% of the volume of our blood, but the specific percentages of each can vary. Hematocrit is the percentage by volume of red cells in your blood.

Because the purpose of red blood cells is to transfer oxygen from the lungs to body tissues, a blood sample's hematocrit can be an indicator of its capability of delivering oxygen. If you have too many red blood cells (high hematocrit), your blood gets thicker and the risk of heart attack or stroke escalates considerably.

Hematocrit levels that are too high or too low can indicate a blood disorder, an elevated risk of dementia, dehydration or other medical conditions. An abnormally low hematocrit may suggest anemia.