A new study suggests depression may soon be detectable through a simple blood test—by tracking how certain immune cells age. Researchers found that accelerated aging in monocytes, a type of white blood cell, is closely tied to the emotional and cognitive symptoms of depression, like hopelessness and loss of pleasure, rather than physical symptoms such as fatigue.

A new study suggests depression may soon be detectable through a simple blood test—by tracking how certain immune cells age. Researchers found that accelerated aging in monocytes, a type of white blood cell, is closely tied to the emotional and cognitive symptoms of depression, like hopelessness and loss of pleasure, rather than physical symptoms such as fatigue.