Quantitative PCR has played a part in the development of what could be the first objective test for major depressive disorders (MDD) in adults, and one that could predict who might benefit from cognitive behavioural therapy (CBT).


Depression is generally diagnosed by an assessment of self-reported and non-specific symptoms, and relies on the patient’s ability to report his symptoms and the physician’s ability to interpret them. Being able to use a blood-based laboratory test could make diagnosis more accurate, track patients’ treatment objectively, and create personalised therapies.

The study, published in Translational Psychiatry, looked at using a blood-based biomarker panel in adult patients with MDD. The team, from Northwestern University, USA, used quantitative real-time PCR (qPCR) to measure RNA markers in the blood of 32 patients with self-reported depression before and after 18 weeks of CBT, and compared these with 32 non-depressed controls. They found nine markers that were different between depressed patients and controls, and saw changes in the levels of some of these markers in patients who had responded to CBT after 18 weeks and were no longer depressed.

“This clearly indicates that you can have a blood-based laboratory test for depression, providing a scientific diagnosis in the same way someone is diagnosed with high blood pressure or high cholesterol,” said Eva Redei, who developed the test and is a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine. “This test brings mental health diagnosis into the 21st century and offers the first personalized medicine approach to people suffering from depression.”

Redei previously developed a blood test that diagnosed depression in adolescents. Most of the markers in the adult depression panel are different from those in depressed adolescents.

According to the researchers, this is the first biological indicator of the success of cognitive behavioral therapy. The new blood test will also allow physicians to use lab tests to determine what treatments will be most useful for individual patients for the first time in depression, based on a distinct pattern or fingerprint of the levels of the nine marker levels at baseline. Because the blood concentration of three of the nine RNA markers remained different in depressed patients and non-depressed controls, even if the depressed patients achieved remission from depression after the therapy, the test may also have potential to be used to indicate a vulnerability to depression.

“Being aware of people who are more susceptible to recurring depression allows us to monitor them more closely,” says  David Mohr, a professor of preventive medicine and director of the Center for Behavioral Intervention Technologies. They can consider a maintenance dose of antidepressants or continued psychotherapy to diminish the severity of a future episode or prolong the intervals between episodes.”

The next step is to assess the test in a larger population, and to see if it can differentiate between major depression and bipolar depression.