In addition to hormone imbalances and shifts in mood, one of the hallmark physiologic changes of depression is the body’s slowed reaction to stimuli. Often, it’s manifested as the change from sullenness to downright indifference. A recent study now supports that lag, as scientists from Linköping University have developed a suicide test that is 97 percent accurate at predicting a depressed person’s risk.

The link between depression and suicide has been known for some time, yet hard data on how to concretely assess a person’s suicide risk has remained light. Simple questionnaires may be effective, but the new blood test, which measures circulation and blood pressure in the person’s sweat glands, has now quantified a previously qualitative analysis.

Published in the Journal of Psychiatric Research, the study involved 783 depressed in-patients in Germany who were tested for hyporeactivity — a measure of slow reaction time. Later assessments of the subjects showed hyporeactivty in 97 percent of the people who committed suicide, compared to only two percent in the people that did not. “The results are so strong that I’m astonished”, said Lars-Håkan Thorell, associate professor in experimental psychiatry at Linköping University, in a statement.

It’s important to keep in mind the risk for false-positives. The test didn’t differentiate between someone moderately depressed and someone who is severely depressed, which means that just because someone shows hyporeactivity doesn’t mean they’re suicidal. Rather, the effect goes the opposite direction: people who were suicidal showed greater rates of hyporeactivity.

“[The test] indicates a certain percent, even if the normal population can have this neurophysical disorder,” Thorell points out. “Everyone who has it is not suicidal — but almost all suicidal, depressed patients have it.” Other measures to keep in mind are the fact that 80.2 percent of bipolar patients showed hyporeactivity, 67.3 percent of depressed patients, and 58.5 percent of other diagnoses. In other words, a very large group of people may show hyporeactivity, and the suicide rate may be very small, yet those who committed suicide nearly always showed hyporeactivity.

Thorell and his colleagues measured hyporeactivity via sensors placed on subjects’ fingers, which would pick up their reaction time to a pattern of tones. When a tone first plays, the subject nearly always reacts. But each subsequent tone yields slower reaction. “A depressed person has a biological inability to care about the surroundings, while a healthy person continues to react,” Thorell said.

Going forward, Thorell will conduct larger studies in 15 other countries to better understand the role hyporeactivity plays in predicting suicidality. What still needs unpacking are the specific differences between those at risk for suicide and the hyporeactivity found in otherwise healthy patients. Someone who is only moderately depressed, or just beginning to show symptoms, may not benefit — indeed, may come into harm depending on the person’s medication — from suicide prevention efforts. Such are the limits of looking backward in a study.

Nevertheless, Thorell remains hopeful given his team’s latest findings. “We can determine very accurately whether a person risks committing suicide,” he said, “which can revolutionize suicide prevention."

 

 

Source: Thorell L, Wolfersdorf M, Straub R. Electrodermal hyporeactivity as a trait marker for suicidal propensity in uni- and bipolar depression. Journal of Psychiatric Research. 2013.