Drug test results question?

I have a client who has an Rx for Adderall. He had a drug test, and obviously tested postitive for Amphetamines. Did a second screen, GCMS, and negative for meth, positive for Amphetamines. The quanity in the test result is 7000 ng/ml, his Adderall Rx is 20 mgs one time a day. His ex is arguing he is abusing Adderall due to the high levels (500 ng/ml is the "cutoff"). Thoughts? Obviously I am seeking expert advice as well, just wanted to see if anyone could guide me. Thanks!