How do you rule out ADD?

Seems like it's almost as easy for adults to get a diagnosis of ADD and a stimulant these days as for Bipolar Disorder and a mood stabilizer. Probably the easiest way is to go to someone who claims to be an ADD expert, maybe get a brain scan with pretty colors. The more expertise the clinician has the more likely they will bestow the diagnosis.

But it also seems to me that an expert should excel at determining you do not have the disorder.

To further this discussion let's borrow some concepts usually applied to laboratory pathology. We call a test, like a thyroid function test, positive when it confirms the presence of the disease and negative when it rules the disease out. So if certain thyroid hormone levels in your blood exceed the normal limits we might call the test positive for hyperthyroidism; otherwise the test is negative. But like a psychiatric diagnostic examination, even including the brain scan de jour, laboratory tests can mislead, in which case we call them false:

• False positive: The test suggests the disorder is present, but it is really absent.
• False negative: The test suggests the disorder is absent, but it is really present.

You may then ask, "But how do we know for sure whether the disorder is present or absent?" This presents more of a problem for ADD than for hyperthyroidism. We can confirm or rule out the latter illness with further objective tests, but there exists no such gold standard or objective test for ADD.

What difference does it make?

One reason experts and amateurs alike tend to diagnose ADD so readily is that a false negative deprives the patient of a potentially very helpful treatment. We tend to like to avoid that by applying looser criteria. But that approach leads to more false positives.

The downside of a false positive usually involves proving someone a potentially addictive or abusable drug they may share with others or use to get high. Having such a diagnosis, even just in an old record, might also prevent you from obtaining something, like a job or insurance. Absent this downside we might just throw stimulants at everyone, and if they like them diagnose ADD, or if they don't tell them they don't have it. But we know that doesn't really avoid the false positives and negatives either. Many people who do not suffer from ADD likely experience stimulants as pleasurable or improving their cognitive functioning and alertness (false positive).

Clinicians still face this person who claims to have a problem and want help. Sometimes we can diagnose an anxiety disorder and treat that, and sometimes we feel confident the patient just wants drugs for the wrong reasons. Maybe we don't pick up a clear history of ADD dysfunction in childhood. But it's hard to say, "You don't have ADD. Go away." unless you can be very confident that you are not looking at a false negative.

I like to think the real experts should have more confidence when they rule out the disorder, but do they? 

How do you rule out ADD in adults?

or

How do you rule out ADD in adults?