A sort of related curiosity are birds: normal blood glucose for a bird is 200 to 300 mg/dl (11-17 mmol, if I converted that right). From an engineering perspective, it makes sense that a creature with the high (and sometimes sudden) energy demands of a bird would circulate a richer mixture. Also from an engineering perspective, the whole system is designed to that spec and birds do not suffer any of the debilitating effects that mammals do from such a high blood glucose (sigh).