Such a test could alleviate the need for costly and inconvenient sleep studies in children who snore, researchers from the University of Chicago and the University of Louisville report in the December 15, 2009, issue of the American Journal of Respiratory and Critical Care Medicine.
A simpler test could also speed up screening, diagnosis and treatment and “ameliorate the overall outcome,” the authors suggest.
“We did not expect that urine would enable us to identify OSA,” said study director David Gozal, MD, professor and chairman of pediatrics at the University of Chicago. “However, the field of biomarkers is rapidly expanding. This opens the way for possible simple diagnostic screening methods in the future.”
Obstructive sleep apnea (OSA) affects an estimated one to three percent of children up to the age of nine. It can lead to cognitive, behavioral, cardiovascular and metabolic consequences. Because there are few pediatric sleep diagnostic facilities, children with suspected OSA seldom get diagnosed promptly and treatment is often delayed.
Pediatricians can’t begin therapy without a sleep study, however. Although 12 percent of children habitually snore, only 25 percent of those children suffer from OSA. Since treatment begins with surgery to remove enlarged tonsils and adenoids, distinguishing between OSA and habitual snoring is crucial.
Gozal and colleagues studied 120 children ages 2 to 9. Ninety of the children were referred to a sleep clinic to be evaluated for suspected sleep-disordered breathing; the other 30 were healthy, non-snoring children.
The children all underwent standard overnight polysomnography and were categorized either as having OSA (60), habitual snoring (30) or no sleep-disordered breathing (30). Urine samples were collected the morning after the sleep study.
The researchers used a sophisticated electrophoresis technique to screen hundreds of proteins in the urine. They found 12 proteins that were consistently higher or lower in children with OSA compared to children who snored or healthy, non-snoring children.
Nine proteins were increased and three were decreased in those with OSA. There was no difference in protein levels between children who snored and those with no obstructive sleep apnea.
Levels of just four of those proteins provided a highly accurate test for apnea and “can potentially be used to screen children with habitual snoring in the future,” the authors wrote.
Several of the proteins that were elevated in children with OSA are associated with inflammation and are considered sensitive indicators of mild kidney damage. The researchers suspect that the “intermittent hypoxia and globally increased oxidative stress and inflammatory processes activated by OSA may lead to mild renal dysfunction.”
The next steps, Gozal said, are to validate these findings in urine samples from many children from laboratories around the country and to “develop a simple color-based test that can be done in the physician office or by the parents.”
Additional authors include Leila Gozal and Jinkwan Kim of the University of Chicago; and Saeed Jortani, Ayelet Snow, Rakesh Bhattacharjee, and Oscar Capdevila of the University of Louisville.