kerrie , i am also CPKU , that stands for classic pku. i think it means we are alittle more rare and sensitive to pku. i have the full defination at home, i will find it and send it to you. i do know that it means treatment is very very importnat not that it isint at anytime but its just the best for us. if u understnad that that good cause i know im not explaining it right. brea could u elaborate till i get home to get the definition?