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A group of Emory University scientists wants to use a sweat test to pre-screen people for PTSD immediately following a traumatic event. They measured hand sweat – an important measure of unconscious physical responses to threat – to see if perspiration would predict PTSD in people visiting the ER immediately following a potentially traumatic event.
More palm sweat did predict greater risks of PTSD down the road for many patients.
But the test also returned false positives, raising potential ethical questions. Trauma is almost ubiquitous to the human experience – but post-traumatic stress disorder (PTSD) is not.
About 20 percent of that 70 percent are thought to develop PTSD, but other estimates suggest that 10 percent of people the world over will develop long-term issues after trauma has passed.
The trouble is working out which 10 or 20 percent will develop PTSD and why.
‘That’s the million dollar question,’ says Dr Tanja Jovanovic, an Emory University psychiatrist who is leading the development of the sweat test for PTSD.
It’s also the subject of much of her research: ‘Determining the biology that puts someone at risk, including possible genetic markers – genes that code for stress response – is an important component,’ she says.
We also know that elements of personal history, such as childhood adversity or abuse and depression, increase the risks of developing PTSD at some point.
But these rather broad risk factors are not yet fine enough instruments to predict PTSD.
So Dr Jovanovic is developing a deceptively simple test: sweat.
Our bodies are equipped with an alarm and response to any kind of danger or threat, called the sympathetic nervous system.
Without us consciously telling it to, the body starts gearing up for fight or flight.
That means that adrenaline surges, heightening our senses and priming our musculoskeletal system to react quickly to whatever might happen next.
Adrenaline is the same hormone that triggers sweat production, but why this is triggered by stress is a bit of a mystery.
The fight or flight response is almost certainly tied to it, so it might make sense for the body to sweat to keep cool in literal fight or flight situations.
But there’s a catch. Though they’re both triggered by adrenaline and both contain water and salt, sweat from overheating and sweat from stress are actually distinct substances, secreted by separate glands.
Nevertheless, for some people, thinking about trauma activates the sympathetic nervous system – more in some than others – and may trigger some kind of sweating.
‘We think a hypersensitive nervous system is one of the markers of PTSD risk,’ says Dr Jovanovic. So she and her team posited that they could measure hand sweat while talking about a traumatic even just afterwards as ‘an early insight into who is going to need therapy and who might not need it,’ she explains.
First, they measured the baseline sweat levels of people who had come into the emergency room after a potentially traumatic event. Then, over the course of five minutes, they questioned the patients gently about what they had just been through.
This element was important because it’s not just that their skin conductance is higher just at resting state, its talking about the memory of the traumatic event, even when it just happened a few hours ago and how active they’re [sweat response] is getting when they’re talking about it.
Resulting baseline and recollection sweat scores were compared, and the test did a pretty good job of screening for people at risk. It was about 85 percent accurate.
But it did return false positives.
Dr Jovanovic says that that’s okay because ‘it’s like a mammogram: there are a lot of false positives, but the cost of missing someone is much greater than missing someone at risk.’
‘You want to weight a test toward being more sensitive rather than less sensitive, as long as it’s a low-cost assessment and you’re identifying the people you want to keep an eye on, it doesn’t cost that much.’Still, she recognizes that they need to continue working on the test’s accuracy.
Dr Jovanovic is acutely aware of the risks of telling someone they are at risk for a debilitating disorder. She draws on the example of disaster relief programs: ‘There was a big controversy with debriefing after a major disaster,’ she explains.
‘Their approach was to tell a bunch of people, en mass, there that they may be at risk for bad things, and that really had negative consequences.’ Some day, if the test makes its way into clinical use, patients would be told that they were at risk for PTSD, but only with the parallel reference to further testing and therapy, Dr Jovanovic says.