Any such test is a long way off, experts say. But the new research, published online Aug. 20 in the journal Molecular Psychiatry, is a step in that direction.
Using blood samples from nine men with bipolar disorder, researchers were able to isolate a group of proteins that rose or fell when the men worsened from having no suicidal thoughts to contemplating suicide.
What's more, a few of those proteins were particularly high in blood samples from another group of men who had committed suicide. It all raises the possibility of developing a blood test that could help psychiatrists gauge suicide risk in patients with bipolar disorder or other mental illnesses, such as major depression.
We're 'not ready' for this test
But nothing like that is "ready for prime time," said Dr. Charles Luther, director of inpatient and emergency psychiatry at Lenox Hill Hospital in New York City.
"We're not yet ready for a blood test to predict suicide risk," said Luther, who was not involved in the study. But, he added, the results are "interesting," and an objective test for gauging suicide risk is needed.
"It's very difficult to pin down risk," Luther noted. Psychiatrists can look at a patient's history and what's happening in his or her life at that moment. Beyond that, Luther said, "all we can do is ask them what's going on in their mind."
The problem is, they may not admit the truth, said study author Dr. Alexander Niculescu, an associate professor of psychiatry at Indiana University School of Medicine in Indianapolis.
"They don't want to be stigmatised, or hospitalised. Or they may not want to be stopped," Niculescu said.
Suicide is, fortunately, relatively rare. Still, "over 1 million people worldwide commit suicide each year, and those deaths are preventable," Niculescu said.
For the new study, the researchers first focused on nine men with bipolar disorder who were part of a larger, long-term research project. During the course of that study, all nine men had gone from having no suicidal tendencies to contemplating or attempting suicide.
Looking back at the men's blood samples, Niculescu's team found 41 proteins whose levels changed when the men became potentially suicidal.
Next, the researchers turned to the coroner's office to get blood samples from nine men the same age who had committed suicide. In the end, six proteins stood out as being strongly linked to suicide risk: They had risen in the nine bipolar patients, and were even higher in the men who'd actually gone through with suicide.
The protein with the greatest change was one called SAT1, which is involved in "programmed cell death" -- where damaged body cells essentially commit suicide. Some of the other proteins are involved in inflammation and the body's stress response, Niculescu said.
It's not clear why the proteins were related to suicide risk. And Luther said the findings do not mean that spikes in the proteins "cause" people to commit suicide. "It's just a correlation," he said, and not a cause-and-effect relationship.
But he and Niculescu said the findings could eventually give some insight into the biology of suicide.
More research needed
First, however, Niculescu said additional studies need to look at women and people of other ethnicities since the men in this study were all white. (One postmortem blood sample was from a black man.) They also need to focus on patients with other mental illnesses, such as major depression, he added.
Dr. Morton Silverman, senior science advisor to the Suicide Prevention Resource Center in Washington, D.C., agreed that the findings are preliminary and limited to this particular group of men.
Another issue, Silverman said, is the way the study defined "suicidality" in the men with bipolar disorder. They were considered to be "high" in suicidal ideation if they had attempted suicide, or if they'd had "any thoughts" about their own death, or wished they were dead. But those are very different states, Silverman noted; someone with a past suicide attempt is clearly at increased risk, while someone who has thought about death may not be suicidal at all.
Still, he praised the "sophistication and creativity" of the work, in finding blood markers that might be associated with "a range of suicidal thoughts, intent or attempts," at least in this group of men.
Even if a blood test for suicide risk becomes reality, it would only be one part of assessing patients, Niculescu said. "You're not just going to rely on a blood test to recommend that someone be hospitalized," he noted.
Instead, he said, a psychiatrist might use the test along with other information on a patient's risk factors, and questions about his current depression and anxiety symptoms.
No single test will ever determine a treatment plan, Luther agreed. "We're dealing with human beings, with complex emotions and experiences," he said. "We need to know more about them than just blood test results."
The National Suicide Prevention Lifeline offers help to people at risk.