What restrictions exist for O negative blood recipients in transfusions?

A person who is O negative can receive only O negative blood (for red cells) because they lack A, B, and Rh D antigens and will have antibodies to A, B and anti-D if exposed. So in red-cell transfusion they are restricted to O negative donor units. 

In urgent situations type O negative may be given to unknown recipients. Also Rh negative recipients must receive Rh negative blood to avoid sensitization. For plasma and platelets other rules apply as above. So an O negative recipient must ensure donor is O negative for red cells.