FRIDAY, Feb. 3 (HealthDay News) -- Depression can be a tough condition to diagnose accurately, but new research suggests that someday a blood test might help.

It's not clear how much the test might cost, and it needs more stringent validation before it will be ready to be used in medical offices. Still, "it appears that these results are promising, after decades of research into finding a biological test for depression," said study author Dr. George Papakostas, an associate professor of psychiatry at Harvard Medical School.

The study was funded by the Ridge Diagnostics Co. and appeared in a recent issue of the journal Molecular Psychiatry.

It may seem like depression is an easy condition to diagnose and doesn't need a test to verify that it exists, but Papakostas said there are several ways that a blood-based depression test might be helpful.

For one, he said, a test could help doctors who aren't as experienced in psychiatric disorders. Also, he said, a test may provide assistance to doctors who aren't sure about the proper diagnosis of a patient: "This could be of help to them, in terms of guiding them in one way or another," he said.

Yet another use for a test would be to verify that a patient has depression, and therefore help him or her accept the diagnosis. "The majority of patients diagnosed with depression have no problem accepting the need for treatment," Papakostas said. However, "there is a minority of patients who feel that validation of an underlying process is helpful," he added.

In their study, Papakostas and his team gave a blood test to 36 patients with depression and 43 people who weren't depressed. The test looked for levels of nine different "biomarkers" in the blood that are associated with depression. These biomarkers are linked to inflammatory processes, the development and maintenance of brain cells, and interactions between brain structures associated with the stress response and other functions.

The researchers found that the test correctly identified patients with depression 91 percent of the time; the rest of the time it gave a false-negative diagnosis (it failed to spot the depression). The test correctly identified patients who weren't depressed about 81 percent of the time, giving false-positives the rest of the time.

The next step is to try to confirm these findings through further research, Papakostas said.

He didn't know how much the test might eventually cost, but he said it won't be as high as thousands of dollars and should be more akin to routine blood tests.

The test appears to detect inflammation in the brain, which has been linked to depression, Papakostas said. "That really doesn't surprise researchers. Chronic inflammation has been tied to a number of other illnesses in the kidneys, lungs and heart," he noted.

One outside expert said such a test would be welcome.

Dr. Michelle Riba, a professor of psychiatry at the University of Michigan who's familiar with the findings, said a blood test for depression could be helpful in several ways.

For one, it would be useful to identify people, especially children and adolescents, who are prone to depression and try to prevent it, she said.

Also, she said, a test could help give physicians insight into how depression treatments are working over time.

More information

For more on depression, had to the U.S. National Library of Medicine.