Billing for Blood and Blood Products Under the Hospital Outpatient Prospective Payment System (OPPS). This instruction provides information contained in Change Request (CR) 3681 which compiles and clarifies Medicare procedures and policies for the billing of blood and blood products in the hospital outpatient setting. In particular, hospitals should note the portions of this instruction that inform them when to use new modifier BL when submitting claims for blood and blood products. Modifier BL (Special Acquisition of Blood and Blood Products).