Certain behavior patterns often precede suicide attempts by people with major depression, suggesting signs that doctors can and should watch out for, a large study suggests.

The hallmarks of suicide risk may include risky behavior, agitated behavior, impulsivity and the presence of "depressive mixed states" that include both depression and mania symptoms, the investigators say.

"The results of this study are important because they may guide clinicians (from GPs to specialists) to which symptoms to pay special attention to and to search for in any depressed patient," Dr. Dina Popovic, psychiatrist at the Hospital Clinic of Barcelona, Spain, told Reuters Health by email.

"Due to the large number of patients in this study, we were able to identify specific symptoms which mostly increase the risk to attempt suicide," said Popovic, who led the study.

Results of the BRIDGE-II-MIX study were released August 30 at the 28th European College of Neuropsychopharmacology (ECNP) Congress in Amsterdam.

The study included 2,811 patients suffering from depression, including 628 with a prior suicide attempt. The researchers tried to find differences in the characteristics and behaviors of those who did and did not attempt suicide.

They found that depressive mixed states, in which a patient is depressed but also has symptoms of excitation or mania, often precede suicide attempts. "In fact, 40 percent of all the depressed patients who attempted suicide had a 'mixed episode' rather than just depression," Popovic said in a conference statement.

The researchers also found that standard psychiatric diagnostic criteria identified 12 percent of patients at risk of such mixed states, whereas the study team's methods found that 40 percent displayed mixed depression.

"This means that the standard methods are missing a lot of patients at risk of suicide," Popovic said.

In a second analysis of the data, the researchers also found that depressed patients who display impulsivity, risky behavior - such as reckless driving or promiscuity - or psychomotor agitation, such as pacing around a room, wringing one's hands or pulling off clothing and putting it back on and other similar actions, had a 50 percent higher risk of attempting suicide than depressed patients without these behaviors.

Mixed depressive states are "hallmarks of bipolarity (and) are not difficult to detect once you know what to look for," Popovic told Reuters Health. "The main difficulty is that these symptoms often won't be spontaneously reported by the patient (e.g. risky behavior), but need to be specifically asked by the clinician."

"This study," she added, "will hopefully increase the awareness of clinicians to which symptoms to look for, even if some of these symptoms have been excluded from the (current psychiatric diagnostic manual)," Popovic said. "If present, they should be addressed from a therapeutic point of view and, in patients at risk, suicidal prevention techniques should be implemented."

"The recognition of increased activation in the context of a severe depression is an important practical challenge," noted ECNP President Dr. Guy Goodwin, a professor of psychiatry at University of Oxford, UK, in a statement. "While many psychiatrists recognize that this constitutes an additional risk for suicide, and would welcome better scales for its identification, the question of treatment remains challenging. We need more research to guide us on best practice."