text: my son has classic pku, he is 21 months old and the amount has not changed, he was born about 6 pounds and is now about 32. the safe range is approximately between \n2 and 10 mg/dl (phenylalanine), your doctor should be keeping a close eye on him, and with regular blood tests (weekly till 2 years)\nlevels should not be to high. i am sure they will tell you if they were concened.\nI live in australia so things may be differant between us, but please if you are at all concerned talk to the doctors/dieticians. good luck.