Peripheral measurement of CNS events (Score 1)

I am an endocrinologist. I see and treat persons with hormonal disorders that can often be diagnosed with measurement of hormones in the peripheral bloodstream. I have long told patients that psychiatric disorders have a biologic basis, but cannot be assessed with a simple measurement of substances that show up in the systemic circulation. I would be skeptical that events (ie measurable substances) beyond the CNS Blood-Brain barrier would show up with sufficient sensitivity and specificity to diagnose a condition that takes psychiatric specialists to assess. I think the most promising means of assessing CNS neurochemistry may be specialized imaging studies like PET scanning of metabolic activity of different regions of the brain. Psychiatry is where endocrinology was 50 years ago. Until we improve means of measuring the biologic basis of psychiatric disorders, I would be hesitant to make ER-based decisions on management based upon a peripheral blood test result.