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 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.
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"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.
SOURCE: http://bit.ly/2IbOxIU Cancer, Epidemiology, Biomarkers and
Prevention, online February 23, 2018.
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