REUTERS: Nearly all the adolescents in an economically disadvantaged, largely minority population in San Francisco who were tested for a tobacco-smoke byproduct showed evidence of regular exposure, a small study found.
Researchers were looking for an accurate marker of tobacco smoke exposure that could also distinguish smokers from those who were just exposed to second-hand smoke. In tests of urine samples from pediatric patients of a public hospital, they found that more than 90 percent were above the cutoff for second-hand exposure.
The marker the study team used, known as NNAL, is detectable in urine for much longer periods after tobacco exposure than cotinine, another compound commonly used to screen for smoking, the authors note in Cancer, Epidemiology, Biomarkers and Prevention.
"Our broad interest is developing ways to screen for secondhand smoke exposure in people seeking medical care," lead author Dr. Neil Benowitz said in an email.
"In adolescents, in particular, we know that secondhand smoke exposure increases the risk of respiratory infections and asthma. In adults, secondhand smoke increases the risk of lung cancer and heart attack," said Benowitz, who is chief of Clinical Pharmacology at the University of California, San Francisco.
A biochemical test of exposure could be used to signal the need for counseling about ways to avoid secondhand smoke exposure, he added.
The researchers measured levels of both cotinine and NNAL in urine samples left over from tests done for other reasons on 466 adolescents. More than 90 percent had public health insurance and 8 percent had no health insurance. Most were Latino, 22 percent were African-American, 11 percent were Asian and 3 percent were white.
"Using NNAL we found that 94 percent of adolescents attending pediatric clinics at Zuckerberg San Francisco General Hospital (the public hospital for San Francisco County) had evidence of secondhand smoke exposure," Benowitz said. This is despite the fact that, overall, less than 10 percent of people in San Francisco smoke cigarettes, he noted.
The researchers also looked at cotinine levels as a biomarker of active smoking and found that about 12 percent of the adolescents had levels high enough to be identified as smokers.
"Cotinine is a breakdown product of nicotine and it indicates smoke exposure, but only over the past few days," Benowitz said. "NNAL differs from cotinine in that it stays in the body for many weeks, making it potentially a more sensitive marker of intermittent exposure."
The group with the highest proportion of active smokers were the African-American adolescents, at about 32 percent, the authors note.
In addition, the level of NNAL in the urine of nonsmokers was highest among African-American nonsmokers, suggesting higher levels of secondhand smoke exposure, they conclude.
"Our study involved primarily Hispanic and African American adolescents from economically disadvantaged families," Benowitz said, "Their exposures are primarily in the home and with friends at parties, clubs etc."
In addition to its small size, the study is limited by the fact that subjects were patients of a single hospital in a city with low smoking rates. They were also seeking medical care, so the authors can’t rule out the possibility that this group had higher than average risk for second-hand smoke exposure. In addition, ethnic minorities made up the majority of the study population, so the results might not be generalizable to all teens in urban areas, the authors note.
Adolescents receiving medical care in public hospitals are at particular risk and could benefit from routine urine screening for exposure to tobacco smoke, Benowitz said.
The study results indicate that either cotinine or NNAL would be suitable for screening, but that NNAL could detect more exposures.