New Blood Test Diagnoses Depression

Geralt. A blood test for depression could also identify those vulnerable to the condition and the treatment most likely to work

Blood markers have been found with the potential to diagnose major depressive episodes, according to a paper in Translational Psychiatry. In the words of lead author Professor Eva Redei, a test using these would “bring mental health diagnosis into the 21st century.” If the test proves reliable, it could also transform treatment and social responses to mental illness. 

Major depressive disorder (MDD) is one of the most damaging conditions in the developed world. An estimated 6.7% of North Americans are affected each year, and this figure appears to be rising.

Underdiagnosis is rife. Moreover, the lack of an objective test has facilitated widespread slurs that diagnosed individuals are faking their condition, or that depression does not exist at all.  Unsurprisingly, few things are as damaging to a person with depression as the disbelief of those around them.

Redei, of Northwestern University, compared 32 patients diagnosed with MDD based on clinical interviews to 32 controls of a similar age. In the process, she identified nine RNA markers distinctive to people suffering from depression. The differences in readings were dramatic, reducing the chances of false diagnoses.

Some of the patients in Redei’s sample were on antidepressant medication, but were still showing symptoms severe enough to be classified as depressed. There was no difference in the blood markers between those on medication and those who were not.

The patients were about to start a study comparing cognitive behavioral therapy (CBT) over the telephone and in person. While this study found telephone therapy as effective as face-to-face, Redei’s observed much more. The markers for those who eventually came to benefit from CBT were different—even before the therapy began—to those that didn’t respond to CBT, providing hope for testing that matches treatments to individuals.

"Currently we know drug therapy is effective but not for everybody and psychotherapy is effective but not for everybody, " said co-lead author Professor David Mohr. "We know combined therapies are more effective than either alone but maybe by combining therapies we are using a scattershot approach. Having a blood test would allow us to better target treatment to individuals."

For those patients who responded to treatment to the point where they were no longer depressed, six of the RNA markers changed to match the controls, but three remained distinctive. "These three markers move us towards the ultimate goal of identifying predisposition to depression, even in the absence of a current depressive episode," Redei says. Not only does the study represent the first biological indicator of depression, the presence of the three markers during remission offers hope that those vulnerable to depression may be able to get preventative treatment, avoiding episodes entirely.

Redei acknowledges the need to replicate the research with more people and with more frequent testing, and is working towards this. She also hopes to test capacity to distinguish forms of depression, such as bipolar II disorder. Drugs given for depression, unless combined with mood stabilizers, may actually increase the risk of suicide when given to people with bipolar disorder.

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