tokens: The Hp2 / Hpdel individuals had an extremely low level of Hp ( mean + / - SD = 0 . 049 + / - 0 . 043 mg / ml ; n = 6 ) , compared with the level ( 1 . 64 + / - 1 . 07 mg / ml ) obtained from 52 healthy volunteers having phenotype Hp2 , whereas the serum Hp level of an individual with Hp1 / Hpdel was 0 .