Depression May One Day Be Diagnosed With a Blood Test

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In case anyone needed more convincing that depression isn’t all in the afflicted person’s head, some new research published today in Translational Psychiatry suggests that traces of the mental illness can be found in the blood. 

Lead author Eva Redei of Northwestern University identified nine markers in the blood that differed in those diagnosed with clinical depression and those who had never been diagnosed with the disorder. (These “markers” are measures of the levels of RNA, the molecules tasked with carrying out instructions transcribed from the DNA.) What’s more, Redei found that this blood test may indicate who will respond to cognitive behavioral therapy, a technique that helps patients understand how their patterns of thinking influence behavior. 

It’s a follow-up to an earlier study she published a few years back, in which she demonstrated that a blood test can diagnose depression in adolescents and young adults. (Younger people with depression have some different blood markers than adults, Redei explained.) Science of Us spoke to Redei about the potential implications of her work.

Can you talk generally about this idea of having an “objective” test for depression? Why is that so important?
Well, I’m sure you are familiar with how depression is diagnosed today. It’s basically a clinical interview between the patient and the physician. These are questionnaires, and either the physician asks the questions and the patient responds, or the patient fills it out by themselves. And I’m sure you have filled out lots of questionnaires in your life. So you know that even in the best of circumstances, there will be room for error. Now, imagine you are depressed, and maybe you are not very communicative. It really can make the diagnosis very difficult and can result in a huge delay in diagnosing depression.

It’s almost absurd to rely singularly on that mode of diagnosis. Imagine you have diabetes. You see a doctor, and the doctor says, “Tell me your symptoms,” and you tell them, and that’s the only method of diagnosing diabetes. If you have symptoms for some physical ailment, you go to a physician, and you get a complete physical, a blood test — whatever else is needed for the diagnosis. And that’s not what’s happening with any psychiatric illnesses. There are no objective tests that can help a psychiatrist, or any other health provider, with the diagnosis.

How does this blood test work?
It’s pretty simple. The blood is collected, much like any other form of blood test, and then from that we measure the level of these nine markers and compare those levels between the depressed and the non-depressed. So, just like you have a normal level of blood markers for, say, cholesterol, it’s the same here.

There’s a lot of concern about overdiagnosis for psychiatric illnesses already. How do you think your findings might affect that issue?
People who worry about overdiagnosis — they are probably right, and they are probably wrong. Because there is potentially a problem with underdiagnosis, too. In the elderly, for example – we say, “Oh, you’re just old. You don’t have any energy, and you don’t want to do anything — you’re just old.”

Plus, we know that the earlier the diagnosis, the more likely that the patient will get better, faster — that’s as true with depression as it is for things like cancer, or tuberculosis. Our problem is that we still think of this divide between physical illnesses and mental illnesses. It’s like we think our brain is not part of us.

If a blood test for depression became widely used, could it help to change the way we view mental illness?
Well, I hope it changes a lot. I do hope part of the stigma is because there is no objective test. Imagine if you can go to your primary care physician and say, “I really feel that I might be depressed, just run a test and let’s discuss it.” It’s very different than if you have to go to the primary care, then go to the psychiatrist, then go back again. And so maybe in the future, it could be that the first round of screening for depression — just like with any other illness — could be with your primary care physician. Although, this is not meant to replace the psychiatrist, by any means. The point is to help and aid the diagnosis.

And if you have an objective test, then nobody can say, “Oh, just get yourself together,” or “Snap out of it” — you know, the classic statements.