Blood or the components of blood are used to treat patients with medical conditions such as anaemia, cancer blood disorders, and those having surgery.
Blood is usually separated into its individual components or parts, so a patient can be given the particular component they need.
This makes the most of every blood donation, as the components in one unit of blood (or one donation) can be used to treat different patients.
Donated blood or components are given to a patient in a blood transfusion. Blood transfusions are given via an intravenous line into a blood vessel.
How blood was used in 2014, according to hospital usage:
Usage varies between hospitals depending on their particular specialties.
NHS Blood and Transplant works closely with hospitals to make sure valuable blood donations are used appropriately.
The demand for blood from hospitals has fallen due to increased efficiency, but new donors are always needed to make sure there is enough blood to treat those who need it.
Blood can be vital for people with medical conditions or who are having surgery. But blood transfusions can also improve the quality of life for people whose illness has no cure.
Karen Clarke, a community nurse who gives transfusions to terminally ill people in their own homes, says: 'These vital transfusions give patients a better quality of life and the energy and ability to enjoy this precious, final time with their families'.