Scientists have developed the first blood test to diagnose major depression.
The landmark test could give psychiatrists a more objective way to identify different types of depression in their patients, and would be especially helpful in designing treatments for depression in highly-vulnerable teenagers.
The blood test is not designed to determine whether a teen is at risk for the condition or already suffers from major depression. That's something psychiatrists can do, using traditional subjective analysis, during their patients' office visits.
Rather, says Eva Redei, a professor of psychiatry at Northwestern University's Feinberg School of Medicine in Illinois, the new blood test is the first to identify the many different types of major depression, from bipolar disorder to depression driven by severe anxiety. She says this additional information can help doctors tailor therapies for each patient.
"The test probably can identify subgroups of depressed patients, which is the aim in define[ing] the best treatment," Redei says.
Statistics show that depressed teenagers are at particularly high risk of suicide, so there is an urgent need for a test that can zero in on the precise nature of their depression and suggest the most appropriate treatments.
Redei had previously discovered 26 genetic markers, or substances in the blood, that appear to be elevated in depression. She says everyone has the markers, which she likens to those that indicate levels of blood sugar and cholesterol, and the depression markers can be in the normal range or elevated.
That's what Redei and her colleagues discovered in their study of blood markers in a group of 14 male and female adolescents, aged 15 to 19. They had been diagnosed with, but not yet treated for, major depression.
The study also included 14 healthy volunteers. In the blinded study - where researchers did not know which of the subjects had a mood disorder - investigators found they were able to differentiate between the two groups on the basis of 11 genetic markers in their blood.
Among depressed teens, researchers found 18 of the 26 blood markers could tell which participants had major depression and which also suffered from depression plus an anxiety disorder.
Patients with depression are treated with a variety of medications but, according to Redei, treatment is not always effective because one-size does not fit all.
"We can't choose a treatment at the moment because...we can't objectively diagnose how many kinds of depressions there are, what are the characteristics, and so on," Redei says.
The new test will enable that objective diagnosis. But Redei believes the markers she's discovered could be just "the tip of the iceberg," because depression is such a complex disorder. And she says further study should help scientists more precisely identify which markers are positively associated with each subtype of depression.