WASHINGTON (AP) -- The Institute of Medicine recommended Friday that soldiers returning from Iraq and Afghanistan undergo annual screening for post-traumatic stress disorder and that federal agencies conduct more research to determine how well the various treatments for PTSD are working.

Of the 2.6 million service members deployed to Iraq and Afghanistan, it's estimated that 13 percent to 20 percent have symptoms of PTSD.

Federal agencies have increasingly dedicated more resources to screen and treat soldiers, but considerable gaps remain, according to the Institute of Medicine, an independent group of experts that advises the federal government on medical issues. Its recommendations often make their way into laws drafted by Congress and policies implemented by federal agencies.

Barely more than half of those diagnosed with PTSD actually get treatment, often because many soldiers worry it could jeopardize their careers. Also, when soldiers do get care, they're not tracked to determine which treatments are successful in the long-term.

The Department of Defense provides medical care to active members of the military and the Department of Veterans Affairs cares for those who no longer serve. Sandro Galea, the chairman of the IOM panel, said both departments offer many programs for PTSD.

"But treatment isn't reaching everyone who needs it, and the departments aren't tracking which treatments are being used or evaluating how well they work in the long term," said Galea, a professor and chair of the epidemiology department at Columbia University. "In addition, DOD has no information on the effectiveness of its programs to prevent PTSD."

The report concludes only the first phase of the Institute of Medicine study. The panel is hoping to release a second report in 2014 that will provide more specifics about the number of service members and vets who have PTSD and the outcomes and costs of their treatments.

Nick Colgin, who served for 15 months in Afghanistan as a combat medic, suffered a traumatic brain injury after a rocket-propelled grenade slammed into his Humvee. While he showed symptoms of PTSD upon his return to civilian life, he waited to get treatment until just last month.

"I just didn't want anyone to know I had that issue. I didn't want to know myself," said Colgin, 27, now living in New York City and working with the advocacy group Iraq and Afghanistan Veterans of America.

Jason Hansman, the group's membership director, said the stigma of seeking treatment is even more prevalent among those on active-duty.

"A lot of people believe their career will end if they seek treatment," Hansman said.

In a recent speech to mental health provides, Defense Secretary Leon Panetta said commanding officers must make it understood that seeking help for the stresses of war should be seen as a sign of strength rather than as a sign of weakness.

PTSD is triggered by a specific traumatic event, such as being in combat or witnessing death. The symptoms of the illness include a numbing of emotions, difficulty concentrating and exaggerated startled responses to events.

The institute recommended therapies supported by robust evidence, such as working with patients to change their thinking and emotional responses to stress. But the committee's analysis of other innovative treatments, including yoga, acupuncture and animal-assisted therapy, is hampered by a lack of evidence on their effectiveness.

Galea said that the two departments have been under quite a bit of pressure to get programs up and running to deal with the growing number of vets with PTSD.

"There hasn't been as much premium placed on tracking than there has been on implementing treatment," Galea said.

The panel praised the two departments for issuing joint guidelines for managing PTSD, but it's unknown whether their providers adhere to the guidelines. The panel said that primary care doctors within the VA screen Iraq and Afghanistan veterans annually for symptoms of PTSD, and it recommends that the Defense Department do the same.

The panel said it is hopeful that the departments will make more use of therapy through videoconferences that will allow patients in remote locations to get care.

The panel also called for more research to shed light on the brain's defense mechanisms for stress, identify factors that can influence the timing and severity of symptoms and identify signs that could help lead to earlier diagnosis and more precise drug treatments.

The report said that the VA treated more than 438,000 veterans for PTSD in 2010, showing evidence of the widespread scope of the problem. Similar numbers are not available for the Defense Department.

Cynthia O. Smith, a DOD spokeswoman, said the department has already taken steps to address some of the issues raised in the report.

"The department recognizes the need for continued improvements," Smith said.

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