US researchers have developed a new hormone-based test that can better distinguish between the symptoms of depression and schizophrenia.

Depression is thought to affect over 300 million people worldwide and schizophrenia affects as many as 51 million people.  Clinically, it is difficult to distinguish between these two diseases in their early phases, because symptoms are non-specific and relatively mild.  In the study, led by researchers from Yale University in Connecticut, US, the researchers infused patients with a high concentration salt solution to induce the release of the hormone arginine-vasopressin (AVP), and then measured the level of the hormone in their blood. 

The results, reported in Experimental Physiology, revealed that AVP release can distinguish schizophrenia from depression.
Depressed patients showed an increased release of the hormone, while patients with schizophrenia showed a decreased response. 

Further, the novel method will help identify people whose depression or schizophrenia involves signalling via a receptor called NMDAR, and differentiate between the two diseases.  In patients with schizophrenia the NMDA receptor signalling may be decreased, while it might be high in those with depression. 

This hormone test may be a simple way to distinguish and identify patients with NMDA receptor malfunction in each disorder, the researchers said.  "This is the first objective, physiological marker for two major psychiatric disorders that, once fully developed into a clinical test, can allow for earlier and more accurate diagnosis, and selection of more appropriate medications for patients," said Handan Gunduz-Bruce from Yale University.

Distinguishing this specific form of these diseases could allow for earlier and more accurate diagnoses as well as more targeted treatment, Gunduz-Bruce added.