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A Blood Test for Depression

A commercial test could let doctors easily screen for major depressive disorder.

Doctors may soon have a more objective way to diagnose and treat depression: a blood test that provides a score between one and nine, with higher scores correlating with an increased probability of a patient having major depressive disorder.

Developed by Ridge Diagnostics, based in San Diego, the test measures changes in 10 biomarkers in the blood and feeds the results into an algorithm that assesses four different body systems to compute the final score.

While advanced blood tests and imaging scans can reveal many diseases at their earliest stages, diagnosing neuropsychiatric disorders typically requires an expert to assess how many subjective symptoms a patient exhibits. As a result, many patients are misdiagnosed or never diagnosed. In 2005, Harvard researchers published a study that indicated that more than 20 million people in the United States suffer from mood disorders, but only about 50 percent have been diagnosed and are being treated.

Doctors have been searching for an objective, biological test for depression “ever since the beginning of clinical psychiatry, 50 or 60 years ago,” says George Papakostas, an associate professor of psychiatry at Harvard Medical School and director of Treatment-Resistant Depression Studies at Massachusetts General Hospital.

Scientists have tried various approaches, including genetic tests, tests that measure hormone stress responses, or brain imaging. They’ve measured possible imbalances in neurotransmitters such as serotonin, norepinephrine, and dopamine, and even measured vocal cues. “There are some signals,” Papakostas says.”The problem thus far is that if you looked at a single element, a single marker or disease area, the signal was weak.”

Ridge’s test  amplifies that signal by bunching several markers together. The company’s scientists screened more than 100 biomarkers to select the combination of 10 for its depression test. These markers are related to systems known to be affected in depression, specifically the metabolism, immune system, nervous system, and hormones produced by the hypothalamus, pituitary gland, and adrenal glands.

Ridge CEO Lonna Williams says the company has validated the biomarker panel and its algorithm through eight studies done on several hundred patient and control samples. To date, they have shown that the blood test results correlate with diagnoses made using the mental health gold standards—the DSM-IV criteria and the Hamilton Depression Rating Scale—almost 90 percent of the time.

Papakostas has led controlled studies of the blood test as a paid advisor to Ridge Diagnostics. “This test appears to be promising,” he says, but cautions that, “thus far, it’s been used as a  research tool.” The next step, he says, is to apply the test on a larger scale and in the community to validate its usefulness as a screening tool. 

“The benefit of this kind of screening tool is …to apply this where you don’t have anyone qualified to screen for depression,” Papakostas says, such as rural communities where mental health professionals are scarce, or in primary care offices, to see whether a patient needs a psychiatric referral.

Ridge has already begun marketing the test in a limited geographic area on the basis of existing results. Physicians in North Carolina and in Southern California, where the company has its lab and headquarters, can order the test now; the company chose these areas so its staff can work closely with doctors using the test.

Williams says that Ridge has also undertaken case studies to see whether its test can help doctors encourage people to seek psychiatric treatment and to stick to an antidepressant regimen. The company is also developing a blood test to monitor antidepressant therapy. The goal, Williams says, is to be able to discern in a week or two whether a patient is responding to a drug, rather than the four to six weeks it can take to see symptom improvement. “It’s very exciting to see the early data from those two studies, because it can make such a difference in the treatment of patients,” Williams says. 

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