Scientists have developed the first biological test for clinical depression.  

Researchers call this development a breakthrough that will help identify and treat depression at an earlier stage.  

Researchers at England's Cambridge University found that teenage boys who showed symptoms of depression and had high levels of the hormone cortisol were 14 times more likely to be clinically depressed.  

This means doctors can definitely identify depression through a simple blood test.  It also marks the first time scientists have shown that a chemical imbalance can cause depression.  

Results of the research were reported Monday.