As with any disease, detecting depression early is critical for reducing suffering and for finding an effective course of treatment. Now, in a study released Tuesday, scientists led by Eva Redei at Northwestern Medicine say it may be possible to test for depression in the blood—and figure out which patients will benefit most from behavior-based therapy as a treatment.

While a blood test alone can only tell us so much, some 26 markers in the blood had previously been associated with depression—something Redei, a professor of psychiatry and behavioral sciences, and her team had discovered in lab animals. They also applied those findings to human subjects, and found that some of those compounds were present in teens with major depressive disorder. This prompted Redei to put their suite to the test with a sample of patients aged 23 year to 80 years recruited from a Northwestern University general medicine clinic.

In her report, published in the journal Translational Psychiatry, Redei focused on nine markers whose levels in the blood differed between people with depression those who were not depressed. Depressed people went on to receive cognitive behavioral therapy, and Redei and her colleagues followed them to see if they could find any additional markers for whether these patients responded well to the therapy or not.

“What we didn’t bargain for, but what we got, was that by looking at [patients’ blood] before they received cognitive behavioral therapy (CBT), we could identify patterns that tell us who will respond to therapy and who will not,” she says. About 60% of the patients did not experience another depressive episode during the study period’s 18 weeks. But 40% of them did, and they showed differences in three gene products that were measured in the blood.

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In addition, the team also found three markers among the original nine that remained different even among the depressed patients who benefited from CBT, and the controls. That suggests these markers could be harbingers of a person’s vulnerability to the mood disorder. In other words, they could be predisposing factors that make depression more likely in the face of stress or anxiety or trauma. Of the remaining six markers in the panel, Redei says they could be useful measures of the changing state of a patient’s depression, similar to fluctuating levels of cholesterol or blood pressure, and they could be a helpful gauge for doctors in figure out how much treatment or medication a patient might need.

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And these genes, she says, “are a complete and utter surprise because they are relatively unknown. Some of them are genes that are known in other areas of science or medicine but have never been associated with depression before.”

That means they could lead to a better understanding of the disease and, possibly, better treatments. “It’s very dangerous to delay treatment,” says Redei. “We don’t want anybody to suffer, so the goal is to develop a Food and Drug Administration-approved test that is very easy to administer anywhere.”

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