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Israeli researchers have developed a blood test that can verify a diagnosis of post-traumatic stress disorder and also evaluate the effectiveness of whatever treatment the patient is receiving for it.

The test, devised by researchers from Rebecca Sieff Hospital in Safed, was developed with the aid of blood samples both from residents of the north who experienced rocket attacks during the Second Lebanon War in 2006 and Holocaust survivors suffering from PTSD. The test measures the presence of a particular type of cell that is part of the body's immune system.

The researchers took blood samples from 33 people suffering from PTSD and compared them to samples from 31 healthy people. This comparison revealed that the quantity of one type of cell, known as gamma delta T lymphocytes, differed measurably between the two groups.

"This is a subset of cells that links the body's inflammatory response to traumas, such as a wound or an infection that results from a traumatic incident, with the body's ability to immunize itself against that factor," said Dr. Ofer Klein, head of the hospital's research unit, who conducted the study with Dr. Igor Krasnov and Dr. Alex Mizruchin.

Previous studies have shown that the immune system is affected by psychiatric disorders such as depression or schizophrenia and scientists have used this result to devise tests for these disorders. A decade ago, for instance, researchers found that depression could be diagnosed via a drop in the level of activity of NK immune cells.

But even within PTSD patients, these higher levels were not uniform: Men were found to have much higher levels than women. "This finding indicates that men experience a higher level of PTSD than do women," Klein said.

This is crucial, because PTSD treatments currently do not differentiate between men and women. The study, however, found that some treatments were less effective on women than on men.

Overall, Klein noted, "the success rates for both pharmaceutical and psychological treatments of PTSD are quite low." He says he hopes the new test can improve this rate by revealing whether a given patient is benefiting from a given treatment. If the gamma delta T level declines, the treatment is working. If it doesn't, then the treatment isn't working and something else should be tried.

The ability to confirm a PTSD diagnosis is also important, he noted, because certain other psychiatric disorders can produce similar symptoms.

The findings were first unveiled at a conference earlier this month to mark the hospital's centennial. The researchers are now trying to expand their sample pool so they can determine whether there are other significant differences among PTSD patients - for instance, between those suffering from a recent trauma and those suffering from a long-ago one.

There has been growing interest in PTSD among researchers in recent years, and the Rebecca Sieff team is not the first to propose a method of confirming a PTSD diagnosis. In March, for instance, a team from the University of Minnesota said they had used magnetoencephalography in an effort to find a pattern of electrical activity in the brain characteristic of PTSD, while last October, another group of American researchers proposed a method based on the rate at which sugars pass through the blood-brain barrier, as measured via positron emission tomography.

But these and other diagnostic tests proposed over the last few years rely on some form of a brain imaging scan. The Israeli team's method, in contrast, requires only a blood test.