Will a blood test for depression make clinician’s diagnosis obsolete? Will a simple blood test guage response to treatment? Will PCPs soon be able to diagnose and treat depression as they do, e.g. high cholesterol, using a simple blood test to assess and treat the condition? The authors of a new study would have you believe the answer to all of these questions is a resounding yes, but the truth is more complicated.

The study, which is titled ‘Blood transcriptomic biomarkers in adult primary care patients with major depressive disorder undergoing cognitive behavioral therapy’,  was published in Translational Psychiatry and has been widely and uncritically reported upon in the media.  Biomarkers are a hot topic in depression studies today as researchers seek objective, biological indicators of the condition.  In this study the authors look at levels of 9 RNA blood markers which carry genetic information to the cells.  

However, there is one problem with the study. It is not credible.  You can read the detailed analysis here ( http://blogs.plos.org/mindthebrain/2014/09/25/critique-claims-blood-test-depression), but here are some highlights:

  • The study is based on an extremely small sample size whose results are very unlikely to be replicated. The study had 64 total participants, 32 patients in the experimental group and 32 controls. Of the 32 experimental patients 10 dropped out, leaving 22 patients in the sample.  Of the 22 that remained, 9 patients were in remission after 18 weeks of therapy and 13 were not.

–The sample is drawn from primary care patients whose symptoms tend to be mild.

–Patients received both medication and CBT treatment, yet the authors claim that the CBT treatment was responsible for the biomarker changes and symptom remission.

Northwestern has publicized the study and put out a video by the authors of the study. Of the video Professor James Coyne of the Department of Psychiatry at University of Pennsylvania said: “I do not know where the dividing line is between unsubstantiated claims about scientific research and sheer quackery, but this video tests the boundaries, when evaluated in light of the evidence actually presented in the article. “

So no, there is not a blood test for diagnosing depression, nor is there likely to be one anytime soon. Like much contemporary biomedical research it is driven by economic motives. The university is looking for money from private investors to conduct research.

While it is possible that some day there might be a blood test for depression, it is not clear to me that a that a blood test would be that useful for the simple reason that a depression diagnosis is easy to make–it can be done in 15 minutes or less by a trained clinician. Tracking patient change with a blood test is cumbersome; and there is easier and quicker solution, just ask a patient how they are doing or give them a quick self report measure to fill out. Furthermore, even if there were a depression blood test, a clinical interview would probably be needed before treatment was started.  The clinician would want to rule out causes such as dementia, substance abuse or bipolar disorder before initiating psychotherapy or anti-depressant medication.  So even a reliable blood test for depression would probably only be useful as a screening tool.

Inadequate depression treatment is a big problem in American healthcare. PCPs, who are the de facto mental health system, can not do the job alone. But rather than investing in blood test for depression, it would be better to use technology to make existing mental health assessment resources more available to the primary care patient.  Many standardized mental health instruments are available online for real-time assessment.  Mental health clinicians can evaluate the patient in the primary care setting with teletherapy.   PCPs can use these tools before they prescribe an antidepressant or make a referral.  Teletherapy and automated assessments can also be used to follow patients after they receive a prescriptions.  Many patients who are prescribed an anti-depressant do not receive adequate followup care in primary care and do not accept referrals to mental health specialists.  Teletherapy and automated assessment of medication compliance and progress can help fill this gap.