Could blood test for bi-polar disorder be a good thing?

My father recently sent me this link to a news story about how they may have created a blood test that can diagnose bipolar disorder.

The article goes over the debate of whether it's a good thing because of the ease to make diagnoses or a bad thing for privacy. I find it hard to believe that most employers would pay to have your blood tested for this kind of thing, but you never know when it comes to that sort of stuff. Overall, I do think it's a good thing. Personally, I would've been appreciative to know of my disorder 2 years earlier when I went to a shrink for depression. It wasn't until I met a fellow bipolar person that I knew what I had. (after all, who goes to a shrink when you're feeling good or great?) Heck, I may have been able to graduate college instead of crapping out during the worst of my mood swings.

The best thing is that it may be very useful for diagnosing children. Without going into much detail (somethings I will keep more private), a blood test may turn out to be extremely useful diagnostic tool for one of my sons. Diagnosing mental disorders depends largely on the patient relaying their feelings and symptoms to the doctor and many may intentionally omit or overlook important information. I think if I could get a proper diagnosis I could save him from a lot of stress and unnecessary strife.

Of course, the real kicker would be if I took the test and found that I have histrionic personality disorder and not bipolar disorder...