article (requires a subscription) about putative blood tests for diagnosing schizophrenia and depression. Because most of my patients have either depression or anxiety, I skipped to the section on a new depression blood test marketed by Ridge Diagnostics. Called the "MDDScore," the test measures 10 biomarkers, including cortisol, brain-derived neurotrophic factor, prolactin, and several other chemicals I never heard of. According to the Psych Times article (which was based on a presentation at the APA's annual meeting in May), the test has been validated by comparing 80 depressed patients with 50 healthy individuals. A test score of 6 to 9 was "highly predictive" of depression, and statistically differentiated the depressed from the healthy.
But I'm skeptical about this test. Why? First, none of the data have been published in a peer-reviewed journal, though I presume some have been submitted. Second, how useful is a depression blood test if all it can do is to differentiate depressed people from healthy people? I'll wager that my teenaged daughter would be just as accurate as the MDDScore in differentiating a depressed person from a healthy person based on a 5 minute conversation. Imagine buying an electromagnetic field detector to determine whether a shirt is red or blue. Sure, it will work, but the eyes can do it more quickly and for free.
Here are a couple of crucial questions for Ridge Diagnostics, and for any company hawking a depression blood test:
1. Can the MDDScore differentiate depression from any other psychiatric disorder, such as anxiety disorders, adjustment disorders, bipolar disorder, substance use disorder, ADHD, and psychotic disorders? I'm pretty certain that the necessary studies have not been done. If the test cannot distinguish different psychiatric problems, then the MDDScore is simply a non-specific "biomarker" for emotional difficulties of all stripes, and would be essentially useless.
2. Does the MDDScore detect depression as well as the PHQ-2, which consists of two simple questions: "During the past month have you felt depressed or down? During the past month have you been bothered by having little interest or pleasure in doing things?" A high score on these two questions is 83% sensitive and 92% specific for depression (see reference here). Can this $745 blood test even approach these numbers?
Until Ridge Diagnostics can provide compelling answer these two questions, the money paid for the test is, more than likely, money down the drain.