The collection of whole blood first involves the screening of prospective donors to ensure that the donation will not be harmful to either the donor or recipient. Nearly all blood transfused today is obtained from volunteer donors. Volunteers are less likely to have transmissible diseases than are paid donors. Volunteers are permitted to donate no more than five times a year, allowing the body time to replenish iron lost in the red cells of the donated blood. Blood banks must determine the blood type. All donated units must also be tested for antibodies to infectious diseases, such as AIDS and some forms of hepatitis.