Even among psychiatric disorders, depression is a difficult disease to diagnose. Its causes remain a mystery, its symptoms can't be defined with precision, and treatments are spotty at best.But that may soon change. Scientists are looking for ways to identify patients with depression as reliably as they diagnose cardiovascular disease diabetes and cancer . A new study takes a significant, though preliminary, step in that direction by demonstrating that a simple blood test can distinguish between people who are depressed and those who are not.The test examined a panel of 28 biological markers that circulate in the bloodstream and found that 11 of them could predict the presence of depression at accuracy levels that ranged from medium to large.And if that were not remarkable enough, researchers pulled off this feat in a group of teenagers, whose angst often defies all efforts at classification.The study, published online Tuesday in the journal Translational Psychiatry , offers hope that doctors can do a better job of helping adolescents whose mood difficulties go beyond those of typical teens, and whose lifelong prospects could be greatly improved by early treatment. What's more, by using objective data to diagnose mental pain, researchers hope to remove the stigma that often prevents patients from reaching out to doctors."Once you have a measurable index of an illness, it's very difficult to say, 'Just pull yourself together,' or 'Get over it,' " said study leader Eva Redei, a professor of psychiatry and behavioral sciences at Northwestern University's Feinberg School of Medicine in Chicago. A federal report released last year estimated that as many as two-thirds of the nation's 2 million depressed teens are too embarrassed or ashamed to get help.The study drew responses of praise and caution from other researchers seeking better ways to diagnose and treat major depressive disorder."This is definitely an encouraging study," said Dr. Andrew Leuchter, a UCLA psychiatrist who is researching ways to improve treatment with genetic testing and was not involved in the new work. Finding a way to intervene with teens would be particularly valuable since a bout of depression early in life makes repeat episodes more likely, and therefore more urgent to treat, he said.The current study focused on teens and "early onset" depression, but the researchers said they hoped to include adults in future testing.Redei's study takes a middle-of-the-road approach to the search for a "biomarker" of depression. Her team did not look for genetic variations that might predispose an individual to depression, nor did it use advanced MRI scans to home in on peculiarities in the way the depressed brain works. Instead, the team focused on the messenger molecules that carry out genetic instructions for producing or inhibiting proteins.The researchers started out with rats, breeding some for their vulnerability to depression and raising others to serve as healthy control subjects. In an effort to tease out the long-term molecular consequences of childhood stress, some rats from both groups spent hours restrained and alone in their cages. After several generations, the researchers identified 11 distinct molecules that were often found in the blood and brains of depressed rats but werelargely absent in the healthy animals.The tests also turned up 15 molecules that distinguished rats who suffered from a combination of depression and severe anxiety from those whose depression resulted in listless, helpless behavior.Then the researchers tested the predictive value of the same biomarkers in a group of 14 depressed teens between the ages of 15 and 19 and a group of 14 healthy control subjects. Sure enough, the teens with depression had significantly higher concentrations of the 11 targeted molecules in their blood. In addition, there were 18 biomarkers that could distinguish between adolescents who suffered from depression alone and those who had depression and anxiety.Dr. Sidney Kennedy, a psychiatrist at the University of Toronto who is leading a project called the Canadian Depression Biomarker Network, said Redei's study was the first to use messenger molecules as biological signposts for depression. As other efforts to find biomarkers mature — including costly brain scans and genetic analyses — those could refine and strengthen a blood test to screen large populations, he said."There is merit in this work," Kennedy added.In the meantime, he praised the study for making a first attempt at one of the field's most ambitious goals: to explain, describe and distinguish among depression's many and varied forms.Redei said her team hoped to perfect the blood panel by testing it in larger and more varied groups of subjects — including those with other psychiatric illnesses, including bipolar disorder , that are sometimes mistakenly diagnosed as major depression.But before any such blood test could go into broad use, she cautioned, scientists would have to show that it could reliably detect the presence of illness without generating too many false positives."The probability that we will be able to put together a panel that's usable is rather high," she said. "This data at the moment truly proves that it can be done." ||||| Blood tests have long been the diagnostic standard for diagnosing teenage diseases, such as mono and diabetes. Now researchers have developed a blood test that can diagnose depression in teens, a step they hope will lead to a better way to identify the disorder in young people. 
 
 Currently, diagnosing depression depends entirely on a patient's willingness to report symptoms -- and a doctor's ability to interpret them. For teens, the diagnosis is particularly challenging, given the natural emotional ups and downs of adolescence. 
 
 "Teenagers are extraordinarily vulnerable to depression," said Eva Redei, author of the study and a professor of psychiatry and behavioral medicine at the Northwestern Feinberg School of Medicine in Chicago. "And there are no objective, biological measures for evaluating them for depression." 
 
 In the study, published today in the journal Translational Psychiatry, Redei and her team developed a test that looks for markers in the blood of teens with major depressive disorder. By studying rats that had genetic and environmental predispositions for depression, the researchers were able to pinpoint 26 markers of major depression. 
 
 They looked for these markers in the blood of 28 human teenagers, ages 15 to 19, half with depression and half without. They found that 11 of the markers showed up in the depressed teens but not in teens without depression. 
 
 They were also able to distinguish different subtypes of depression, successfully identifying teens who suffered from depression alone and depression combined with anxiety disorders. 
 
 "The uniqueness of this study is that we showed that it can be done. The technology is available to make this diagnosis," Redei said. 
 
 Experts say there is a great need to diagnose depression early in life, particularly among teens. 
 
 According to the National Institute of Mental Health, 11 percent of 13- to 18-year-olds develop major depression at some point in their adolescence. Reports from the Substance Abuse and Mental Health Services Administration are slightly lower – in 2008, 8.3 percent of 12- to 17-year-olds dealt with depression. 
 
 The disorder puts teens at greater risk for other health dangers, including substance abuse, physical illness and suicide. Also, when depression begins earlier in life, the chances that it will persist and perhaps worsen in adulthood are great. 
 
 The study is not the first to try to formulate a blood test for major depression. In February, researchers at Massachusetts General Hospital analyzed blood from depressed adults and found that the levels of nine biomarkers differed from those without the disorder. Redei said her test is different because it identifies blood markers not previously linked to depression. 
 
 Some experts are not so sure how useful a blood test can be in identifying and treating teens with depression. The study authors say they are hopeful that a blood test diagnosis for depression will help more teens get the treatment they need. But none of the teens who were diagnosed in the study opted for any treatment. 
 
 "A blood test doesn't show the dynamics of what the particular person is dealing with, where their depression is coming from. You've got to explore it at a much deeper level than just a blood test," said Elaine Leader, a psychiatrist and the executive director of TEEN LINE, a mental health hotline for California teens. 
 
 Dr. Carol Bernstein, an associate professor of psychiatry at New York University Langone Medical Center, said biologic testing doesn't get at the complex interactions of genes, biology and environment involved in depression. 
 
 "I think people are looking for a magic bullet, a single answer. But these disorders are much too complicated," she said. "But certainly the more tools we have the better." 
 
 Redei said developing a blood test is important not just for diagnosing patients, but also reducing the stigma associated with having depression. 
 
 "The fact that there are no objective biological measures for depression is probably a major contributor to the stigma," Redei said. "Once it's a medically proven objectively measured illness, the stigma sooner or later has to diminish or even disappear." 
 
 Redei and her colleagues are currently testing how well the blood test works in adults with depression.
– Soon, you may not have to sit down with a therapist to know if you have depression. A team of researchers has developed a blood test that can identify the markers of major depressive disorder in teens, they say in a study published yesterday in Translational Psychiatry. The researchers focused on teens because they are especially vulnerable to depression, and may be reluctant to report symptoms, but they hope to include adults in future tests. "Once you have a measurable index of an illness, it's very difficult to say, 'Just pull yourself together,' or 'Get over it,'" lead researcher Eva Redei tells the LA Times. They created the test by stressing out lab rats, and identifying "messenger molecules" in their blood that was not in healthy rats' blood. They then tested teenagers, and found that the same molecules were present in those diagnosed with depression. "We showed that it can be done," Redei tells ABC. "The technology is available."