A Northwestern University scientist has developed the first blood test to diagnose major depression in teens, by measuring a specific set of genetic markers found in blood. Current depression diagnosis is subjective, relying on the patient's ability to recount his symptoms and the physician's ability and training to interpret them. Diagnosing teens is an urgent concern because they are highly vulnerable to depression and difficult to accurately diagnose due to normal mood changes during adolescence. The test also is the first to identify subtypes of depression, distinguishing between teens with major depression and those with major depression combined with anxiety disorder. This is the first evidence that it's possible to diagnose subtypes of depression from blood, raising the hope for tailoring care to the different types.