An interesting take on this by a poster on another website:
Truck driver was innocent and a victim of a police chase.
CDL drivers live and die by their blood alcohol/drug content when involved in accidents.
Cops wanted blood to find out if the guy was drunk or on drugs to use to blackmail him if he decides to sue the department for being injured as a result of their high speed chase.
Cop at hospital was there to make sure a blood sample was taken to cover their assess.
Bingo