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Scientists have developed the first blood test to diagnose major depression in teens.

The test could give psychiatrists a more objective way by measuring a specific set of genetic markers found in a patient's blood. It also is the first to identify subtypes of depression. It distinguished between teens with major depression and those with major depression combined with anxiety disorder. This is the first evidence that it's possible to diagnose subtypes of depression from blood, raising the hope for tailoring care to the different types.   

"This is the first significant step for us to understand which treatment will be most effective for an individual patient," said lead author Eva Redei, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine. 

Diagnosing teens is an urgent concern because they are highly vulnerable to depression and difficult to accurately diagnose due to normal mood changes during this age period. The current method of diagnosing depression is subjective. It relies on the patient's ability to recount his symptoms and the physician's ability and training to interpret them.

"Right now depression is treated with a blunt instrument," Redei said. "Without an objective diagnosis, it's very difficult to make that assessment. The early diagnosis and specific classification of early major depression could lead to a larger repertoire of more effective treatments and enhanced individualized care." 

The study subjects included 14 adolescents with major depression who had not been clinically treated and 14 non-depressed adolescents, all between 15 to 19 years old. The depressed and control subjects were matched by sex and race. 

Redei's lab tested the adolescents' blood for 26 genetic blood markers she had identified in previous research. She discovered 11 of the markers were able to differentiate between depressed and non-depressed adolescents. In addition, 18 of the 26 markers distinguished between patients that had only major depression and those who had major depression combined with anxiety disorder.

"These 11 genes are probably the tip of the iceberg because depression is a complex illness," Redei said. "But it's an entree into a much bigger phenomenon that has to be explored. It clearly indicates we can diagnose from blood and create a blood diagnosis test for depression."

"Everybody, including parents, are wary of treatment, and there remains a social stigma around depression, which in the peer-pressured world of teenagers is even more devastating," she said. "Once you can objectively diagnose depression as you would hypertension or diabetes, the stigma will likely disappear."

The study was published Tuesday in the journal Translational Psychiatry.