Hi, I'm a mother of a 6 month PKU daughter, more or less where you stand I don't know if I got it right, but from what I realized during my daughter's first evaluation, there is a rare form (approx.3%) of PKU, where the defect is in the co-enzyme (BH4) and not the enzyme (hydroxylase) that classic PKUers lack. During the test, they give you the enzyme in pills. If you have this type you will respond (lower the phe after 24 hours.). However, there are other problems with this type. In mild and classic PKU, children do not have the enzyme hydroxylase. When you administer Kuvan it acts as a co-enzyme and helps to increase the activity of the hydroxylase, thus giving a greater tolerance in phe. I do not Know if Ive been helpfull, my English is not that great. However, don't be disappointed, the test you had was not the test for response in Kuvan.