Let's go to the article for a quote:
“Patients aren’t sure how ill they really are, and neither is the clinician — sometimes dismissing their symptoms, sometimes overestimating them,” said Dr. Alexander Niculescu, III, a psychiatrist at the Indiana University School of Medicine in Indianapolis, who led the research published Tuesday by the journal Molecular Psychiatry. “Having an objective test for disease state, disease severity, and especially to measure response to treatment, would be a big step forward.”
Absolutely right. Granted, the test that's being discussed isn't actually anywhere near 100% accurate. Rather, it's about 60-70% at best. Plenty of room for false negatives--or false positives, though it would be irresponsible to diagnose an illness based on a single blood test with 60% accuracy.
The problem I have is that instead of cheering that we might finally have a good biomarker for a devastating mental illness, everyone is whining about ethical concerns. Let's think about this. An objective measure of bipolar disorder would not only allow for more accurate diagnosis, but it would give us better treatment benchmarks. It's easy to tell if a drug for hypertension is working; does it lower the patient's blood pressure by a significant amount when compared to a placebo? Evaluating the efficacy of treatments for bipolar disorder essentially comes down to asking patients "so how do you feel?" and hoping they're being totally honest. Is it any wonder why doing research regarding new treatments for the illness is so hard?
But no, nobody seems to be saying "this is amazing!" Instead, they're all complaining about how people with bipolar disorder are going to get discriminated against in hiring or rounded up and thrown into camps.
Let's start from the beginning. In the US, your health information is private. It is protected by federal law. Employers are not allowed to ask questions about any illnesses you may have, nor are health care providers allowed to disclose any information about your health to employers (or anyone else), including what medications you may be taking.
You might be wondering about urine screening for drug use when hiring new employees. Yes, the practice is legal, but laws vary from state to state. You could argue that this provides a foothold for pre-hire blood testing--except for the fact that most of the people whining about the blood testing procedure are saying that it's going to go beyond hiring. They're suggesting that landlords might blood test people before letting them sign leases, or banks might want people to submit blood before they'll hand out loans. You'll notice that none of these entities can legally conduct urine tests. Under current law, even if an employer were able to get a blood sample and test you for illness X or Y, you could sue them if they refused to hire you based on the results of the test--and you'd win.
Being mentally ill is a disability. Discriminating against people with disabilities in the workplace is illegal. It doesn't matter the disability is patently obvious (a person in a wheelchair) or totally invisible (bipolar disorder). As long as you're qualified for the job, that's all that matters--unless the employer wants to risk a huge lawsuit. This isn't likely to change any time soon. The ACLU would throw a fit, for starters.
The ability to definitively diagnose mental illnesses on the basis of a blood test is 99.9% good. Unless all the work of anti-discrimination proponents is suddenly reversed tomorrow, there's no reason to assume that this is going to create a problem. The only reason to think otherwise if you've watched Gattaca in the past week and it's cranked your paranoia setting up to 11.