Subject:
Depression

Short Description:
Can a Blood Test Diagnose Depression?

Background:

Psychiatrists have long wondered whether someday we might have an objective way to diagnose depression, in much the same way an internist orders a blood test or X-ray. A recent article suggests that just such a test might be on the horizon. Is it the real deal?

Investigators obtained blood samples from depressed and non-depressed patients. They measured levels of nine “biomarker” proteins and performed a calculation to get an “MDDScore.” The details of the calculation are undisclosed, proprietary information, but the end result is straightforward: a number on a scale of 0 to 100, where anything over 50 suggests depression. In a pilot study of 36 depressed and 43 non-depressed patients, the average MDDScores were 85.5 for depressed patients and 32.9 for others. A follow-up replication study of 34 depressed patients found an average score of 81. There were a few false negatives and positives, but the sensitivity and specificity were high, at about 91% and 81%, respectively.

Investigators selected the biomarkers from an initial set of 110 candidates because they helped to distinguish depressed people from non-depressed people. Markers included metabolic, inflammatory, and neurotrophic proteins, among others. Interestingly, in the published study, only four markers were consistently (and significantly) different between the two populations. Whether these four were weighted more heavily in the MDDScore calculation is unknown.

While the results are certainly impressive, they should be taken with a grain of salt. For one thing, there’s no known reason why these nine (or in the paper, only four) proteins should be elevated in depression, or whether they normalize with treatment. Also, subjects were all relatively healthy, not taking NSAIDs or antidepressants, and had no other psychiatric complaints or “unstable medical disorders.” The authors also did not control for demographic factors.

Furthermore, the authors point out that the test cannot differentiate bipolar from unipolar depression (although they’re investigating this) or, for that matter, any other psychiatric condition; it cannot be used to predict vulnerability to depression in someone without clinical symptoms; and it does not reflect the severity or prognosis of a patient’s depression. Nevertheless, the article’s sponsor, Ridge Diagnostics, has already begun marketing the test (at $745 a pop) directly to clinicians and patients (Papakostas GI et al, Molecular Psychiatry 2011;online ahead of print).

TCPR's Take:
There may indeed be some biochemical differences between some depressed patients and non-depressed individuals, and this study may give us some early hints. But the question is certainly still in the research stage. Individuals with depressive symptoms but a negative test still deserve treatment, while a positive MDDScore in the absence of subjective complaints presents an entirely different dilemma. Until the science is made a bit more transparent and more data are obtained—preferably with patients that resemble those we see in practice, and with more controls—we recommend that you save yourself the $745 and steer clear of this test.