Blood tests that track how certain white blood cells age may help identify depression by focusing on emotional and cognitive symptoms rather than physical ones. The research, published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences , moves scientists closer to finding a reliable biological marker for depression, a condition that affects nearly one in five adults in the United States. Blood-Based Clues Could Improve Depression Diagnosis Today, depression is diagnosed based on what patients report about their symptoms. Doctors may order lab tests to rule out other illnesses, but there is still no objective biological test that can confirm depression or detect it early. Part of the challenge is that depression does not look the same for everyone. While some people experience physical (or somatic) symptoms such as fatigue, appetite changes, or restlessness, others mainly struggle with emotional and cognitive effects.…