Imagine this: You’re feeling listless, and you’ve barely eaten in weeks. Your sleep patterns are off — you’re either dozing way too little or way too much. Your head is clouded with worries, and your emotions are a jumble of hopelessness, self-hatred and guilt. You head to your primary care physician’s office, and after a diagnostic interview he or she informs you that you might have major depressive disorder. Then, much to your surprise, you’re asked to provide — of all things — a lab sample. Turns out, one of the keys to yielding an accurate diagnosis for your mental disorder might not lie in just your answers to the doctor’s questions. It might also lie in your blood.

While surreal, this scene from the doctor’s office might actually be closer to reality than anyone imagines. Researchers from Northwestern University recently announced they’ve developed a blood test designed to screen for depression — and upon replication, they hope for it to someday become a U.S. Food and Drug Administration-approved lab procedure. An objective clinical diagnosis, they say, could help doctors pinpoint patients’ depression with efficiency and accuracy. It could also help both identify people who are vulnerable to depression — even if they haven’t experienced it yet — and allow doctors to tailor certain types of treatment to individuals.

Read: [Have You Been Screened for Depression Today?]

Published in the journal Translational Psychiatry, the study compared blood samples from 32 adult patients who had been traditionally diagnosed with clinical depression with 32 adults who were not depressed. In the samples, they analyzed levels of nine blood biomarkers — the molecules that help process the DNA genetic code and perform its instructions — and discovered the levels were different in the patients suffering from depression. This finding, says study co-author David Mohr, could help doctors detect the presence of depression in a way that’s more clear-cut than self-report evaluations based on general symptoms listed in the Diagnostic and Statistical Manual of Mental Disorders.

“Depression, like a lot of mental health problems, is diagnosed today primarily on the basis of non-specific symptoms — kind of where medicine was 80 or 100 years ago,” says Mohr, who’s the director of the Center for Behavioral Intervention Technologies at Northwestern’s Feinberg School of Medicine. “We assess for low moods, motivation, changes in sleep, changes in appetite. But those [symptoms] are also common to many mental health disorders, as well as many other diseases. So having a screening test that can be used to facilitate the identification of depression could have huge implications for treatment.”

Read: [How to Talk to Kids and Teens About Mental Illness]

Depression is often misdiagnosed — or under-diagnosed — for many reasons, Mohr says. For one thing, patients often under-report or don’t fully explain their symptoms. Additionally, a rushed primary care physician might not have the background or training to properly assess a patient for major depressive disorder, much less the time to sit down for a 20-minute mental health evaluation. And patients with potential mental health conditions are likely to have physical problems, too — ones that are more visible and command a doctor’s attention. Due to these occurrences, the period between the beginning of symptoms and an official diagnosis can range from two to 40 months, as the study points out.

“The longer depression is not treated, the more difficult it is to treat,” says Eva Redei, the study’s lead author and David Lawrence Stein Research Professor of Psychiatric Diseases Affecting Children and Adolescents at Northwestern’s Feinberg School of Medicine. “There’s also a higher chance of suicide, and adverse effects in the person’s work, environment, home environment, social structure — everything.”

A lab test could expedite the diagnostic process, Redei says. But perhaps just as important, she says, is that the test’s clinical, unbiased nature could help alleviate prejudice toward mental illness.

“Depression is a disease, but we don’t treat it like one,” Redei says. “Making [testing for it] objective is extremely important because that would eventually eliminate stigma and the distinction between mental health and physical health.”

Read: [Coping With Depression at Work]

One of the study’s interesting facets — which surprised Redei, a neuroscientist — was that cognitive behavioral therapy actually seemed to change the biomarkers in the blood. All the patients in the “depressed” group met and spoke with a therapist. After more than four months had passed, the blood test was repeated on 22 of them. The patients in this group reported in clinical follow-up interviews that they were no longer depressed; they also had changes in their RNA markers, indicating that they benefited from this type of treatment. However, three of their biomarker levels still weren’t the same as those of non-depressed patients, suggesting some individuals might be more genetically susceptible to depression than others.

Also, the researchers say, the blood test was able to predict who would get well from cognitive behavioral therapy after they observed a distinct pattern, or “fingerprint,” of the nine markers at baseline in patients who found relief.

These findings might allow scientists to identify who responds to various therapies or medications. “I think this opens the possibility to begin to look at whether there are biomarkers that may be able to predict response to a behavioral treatment like cognitive behavioral therapy vs. [medicines] — people who maybe do better on pharmacotherapy or other forms of treatment,” Mohr says.

Mohr does make a few caveats about the study. For one, depression is a tricky, multi-faceted disorder that’s difficult to diagnose. It has biological, psychosocial and social components; while a blood test could “greatly facilitate” the identification of depression, it’s not a disease that can be completely encapsulated in a test tube. Additionally, Mohr notes, the study was conducted in a small group of subjects. While both he and Redei hope to reproduce the results in a larger sample size, more studies remain between now and the test’s potential migration to the doctor’s office.

“What we would like to do is to move on to conduct a larger study, so it can become available in clinics,” Redei says. “Then we want to conduct studies to see whether we can differentiate different types of depression — and, of course, we would really like to eventually [find] novel drug targets for depression. Personalized medicine is what we are trying to achieve.”

Read: [How to Find the Best Mental Health Professional for You]

Despite its limitations, however, the study does “represent a significant step forward,” says Andrew Leuchter, a professor in the department of psychiatry and biobehavioral science at the Semel Institute for Neuroscience and Human Behavior at the University of California-Los Angeles. Redei and Mohr “looked not just at genetic variations, but how genes are turned on and off with the illness of depression and in response to treatment,” he says. “That helps for us to move closer to understanding the dynamics of treatment, how it works and what treatments might be most effective.”

“I’d like to see larger sample sizes, because that’s the kind of thing that gives us more confidence,” Leuchter continues. “But for a preliminary report, this is encouraging.”

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Could a Blood Test One Day Detect Depression? originally appeared on usnews.com