A new study suggests that simple, inexpensive blood tests performed while patients are on the operating table could predict how well they will recover months after they leave the hospital.

The study, conducted at Stanford and Yale Universities, found that patients whose immune systems responded to the stress of surgery by mobilizing large numbers of pathogen-fighting cells and redistributing them to skin and other tissues recovered more quickly and completely than those whose immune system showed little or no reaction. The researchers also found that men were more likely than women to mount the beneficial stress response.

“One of the beauties of the tests is that it's so easy,” Esther Sternberg, MD and section chief at the National Institute of Mental Health, was quoted as saying. “The information is completely available pre- and post-surgery.”

Firdaus Dhabhar, PhD and Stanford associate professor who authored the paper, was quoted as saying that short-term stress launches the fight-or flight response, which he described as one of nature's fundamental survival mechanisms. “In an evolutionary sense, why would a gazelle's immune system be suppressed when a lion is chasing it? This is a time when the gazelle would need a robust immune response to protect it from wounding or infection,” said Dhabhar.

Instead of suppressing immunity, short-term stress acts like a call to arms, Dhabhar said, sending immune cells to at-risk tissues and preparing the body to defend itself.  But could that mustering of the troops be clinically beneficial in humans? To find out, Dhabhar chose a stressful situation that would require physical healing afterward – knee surgery.

To ensure the surgical procedure would be as consistent as possible, all of the surgeries were performed by Peter Jokl, MD, professor and vice chair of orthopedics and rehabilitation at Yale University. Three to 10 days before the surgery, patients gave blood samples to establish a baseline count of immune cells in their blood. Then, on the morning of surgery, the researchers took another blood sample just before the administration of anesthesia, looking for an increase in immune cells in the bloodstream.

The idea, Dhabhar said, was that patients would be somewhat anxious about the impending surgery, triggering the short-term immune response. The patients gave a final blood sample after surgery while in the recovery room.

From these samples, researchers measured the immune response of each patient. Patients who showed the positive stress response during surgery showed increased recovery as early as one week post-surgery compared to low responders, an effect that carried all the way through the study period. One year later, high immune responders showed marked increase in recovery over low responders, who never recovered as fully as their stress-adaptive counterparts.

The researchers also discovered a gender disparity. Women were less likely to show an adaptive response than men. On average, their lymphocyte redistribution numbers were nearly four times lower than that of their male counterparts.

SOURCE: Journal of Bone and Joint Surgery, December 1, 2009