HCT in a blood test is hematocrit, the percentage of the blood made up of red blood cells, says MedlinePlus. Normal hematocrit results are 40.7 to 50.3 percent for males and 36.1 to 44.3 percent in females. Newborns have slightly higher levels than adults, and infants have slightly lower levels.
The HCT blood test is done by putting a sample of the patient's blood in a test tube and placing it in a centrifuge, says Mayo Clinic. Anticoagulant is added to the blood to prevent it from clotting, states Healthline. The centrifuge spins the blood in the test tube very quickly. This motion separates the blood into plasma, red blood cells and other blood cells. This helps the physician determine the volume of red blood cells in the blood.
Potential causes for low hematocrit include anemia, leukemia, overhydration, malnourishment, bleeding, destruction of red blood cells, and not having enough iron, folate, vitamin B-12 and vitamin B-6, explains MedlinePlus. High hematocrit levels may be the result of congenital heart disease, scarring of the lungs, dehydration, bone marrow disease and low blood oxygen levels.