The FDA has approved a new test, called NEBA, to help in the diagnosis of ADHD. It uses an EEG to measure the ratio of beta and theta brain waves, which has been shown to be higher in people with ADHD:
However, he added, "it is doubtful that this EEG test newly approved by the FDA will be as accurate and reliable as clinicians and families would ideally want.
"Given concerns among the public and some professionals about the steady increase in the number of children and adolescents being diagnosed with ADHD, it would be wonderful if clinicians had an objective test to assist in the diagnostic process," Adesman said. "Although this new EEG test may prove helpful to clinicians, neither parents nor professionals will be able to rely upon it as a standalone 'litmus test' for whether a child has ADHD."
Adesman also noted that the FDA has approved other "objective" diagnostic tests for ADHD that have not become a common part of diagnosing the disorder, and the fate of the NEBA system remains to be seen.
Read the complete article at: http://health.usnews.com/health-news/news/articles/2013/07/16/fda-approves-brain-wave-test-for-adhd 
I think it doesn't hurt to have more diagnostic tools since it's so complicated to diagnose ADHD. While this test isn't standalone, it's just another tool they can use in conjunction with other testing.
What do you think?