At the present time, a diagnosis of depression comes after the patient completes one or more questionnaires that gauge a person’s mood or emotional state of mind. Behaviors such as sleep habits, anger, and the ability to focus are considered. The diagnosis is subjective at best, leaving doctors and patients alike wishing there was a more concrete way to make a diagnosis, such as a test that provides a definitive conclusion.

Researchers in Vienna may have found just the test that’s been missing. They’ve discovered a marker in the bloodstream that can be measured by analyzing a simple blood sample. This marker is linked to a neural network in the brain that regulates one’s self-reference function.

The two lead Austrian researchers — Christian Scharinger and Ulrich Rabl — are affiliated with the department of biological psychiatry at the Medical University of Vienna (MedUni Vienna). The research team consisted of researchers from the Vienna University as well as colleagues from Germany.

Their 48 study participants were all physically healthy and between the ages of 18 and 45 years old; 31 were female. All study participants were right-handed, all of European ancestry, and German was their native language. None of the study participants had a history of medical or psychiatric illness or was diagnosed with any illnesses at the time of study.

The neurotransmitter, serotonin, is sometimes called the happiness hormone. A specific protein in the membranes of brain cells — serotonin transporter (SERT) — regulates how fast or how completely serotonin passes from one brain cell to the next along with a neural network. Depression is associated with a lack of serotonin and the most widely prescribed antidepressants in use today — serotonin reuptake inhibitors — target the SERT.

The brain isn’t the only organ containing SERT; the intestines and other organs have the transporter protein, too. So does blood. In the bloodstream, SERTs regulate the amount of serotonin in the plasma at any given moment.

A certain network in the brain, a depression network said to be the “default-mode network,” is most active when a person is at rest. It also processes the content of the inner self-reference conversation that plays out in everyone’s thoughts.

In an emotionally stable individual, the activities of the brain during concentration, such as when performing complex thinking or physical activities, suppress this depression network. People who are depressed have difficulties turning off this network, which makes it difficult to concentrate but it also promotes negative thinking and dwelling on negative thoughts (rumination).

The MedUni Vienna researchers used functional magnetic resonance imaging and pharmaceuticals to document how closely related the depression network in the brain is to serotonin levels in the bloodstream. The faster the uptake by the SERTs in blood platelets, the more active the depression network in the brain.

The research team describes its study as the first to use a blood test to predict the activity of the brain’s major depression network. They suggest a blood test to diagnose depression could become a reality “in the not too distant future.”

Source: Scharinger, Christian, et al. “Platelet Serotonin Transporter Function Predicts Default-Mode Network Activity.” PLOS / One. PLOS. Mar 25, 2014. Web. May 14, 2014.

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