Can a doctor who's already been prescibing me adhd medicine try to retest me?

I was tested when I was about ten and diagnosed with ADHD, about 2 years ago I had a doctor prescribe me with out any testing to my medicine. I don't have health insurance but I pay what it cost any ways. Just recently he asked me to have my old doctor who did diagnose me to fax over the records, so I did. Then today his nurse called me and asked me to come in tomorrow. I asked her what the reason was and she just said she wasn't sure but that he left a note for her saying to have me make an apointment as soon as possible. Any ideas on what the reason might be??