Possible Clues:

• Rare blood type, for short
• Uncommon blood type: Abbr
• Rare blood type, briefly
• Uncommon blood type, for short
• Rare blood type: Abbr
• Blood type for about 6% of the U.S. pop.
• Rare blood type, informally
• Blood type for just over 6% of the U.S. pop
• Uncommon blood type, briefly
• Rare blood type: Abbr.