Researchers at Northwestern University in Chicago have developed the first blood test to diagnose depression in adults.  In a study published this month in Translational Psychiatry, scientists identified depression by measuring the levels of nine RNA blood markers -  molecules which act as messengers to interpret DNA genetic code and carry out its instructions. For the study, researchers compared blood samples from 32 clinically depressed patients with samples from 32 people who were not depressed, and found a significant difference between the two groups in the levels of said RNA blood markers. The test further predicts how those suffering from the condition might be treated; indicating which subjects would likely benefit from cognitive behavioural therapy. The breakthrough research means that the biological effects of said therapy could also be measured by testing the blood again following cognitive behavioural therapy. Results showed that the levels of markers changed in patients who had the therapy for 18 weeks and were no longer depressed. Put plainly, this means that therapy which acts to change the thoughts and beliefs of adults suffering from depression has been shown to result in a measurable difference in RNA blood levels and remission of depression. Co-author of the study and Professor of Psychiatry and Behavioural Sciences at Northwestern University Feinberg School of Medicine, Eva Redei explains: "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." "This test brings mental health diagnosis into the 21st century and offers the first personalised medicine approach to people suffering from depression." The approach is revolutionary in the field of mental health, as accurate diagnosis has is very difficult when it is based on patients' self-reporting. It is hoped that the test also will help to remove some of the stigma of depression, as it's sadly still the case that some people think depression is just a sign of "weakness", whereas a scientific test would afford definitive proof that there is a biological issue.