. >> reporter: psychiatry professor and va neuroscience mark resnick said the biomarker involves a specific protein found in our brain and blood. >> what we found is that when you're depressed, it gets stuck in a gooey mass in the membrane. >> reporter: a simple blood test would detect the biomarkerer and may give those struggling the evidence they need to seek help. >> it's not just in my head, it's in my blood. >> reporter: with suicide race rising, the benefit of a blood test to diagnose depression would be revolutionary. >> just really underscores and validates that depression is -- has a biological origin. it's a medical condition. >> reporter: she says it's not mental health professionals but primary care doctors who prescribe the majority of antidepressants. >> prime care is real shrine as the third line of defense for suicide prevention so a tool like this, a relatively easy blood test, can really aid in that prevention strategy. >> reporter: the recently published study of less than 100 people found the biomarker may be able to determine if an antidepressant was working, maybe as s