We don't have synonyms for o-grade yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are no, so and do.
(n) :
(uncountable) A blood type that lacks A or B antigens and may only receive transfusions of similar type O blood, but may donate to all (neglecting Rh factor). Synonym: universal donor.
(n) :
(uncountable) A blood type that lacks A or B antigens and may only receive transfusions of similar type O blood, but may donate to all (neglecting Rh factor). Synonym: universal donor.