Measuring cotinine is a widely used method for assessing nonsmokers' exposure to second-hand smoke, Dr. Wilson and colleagues noted in the March issue of CHEST.

Previous studies have shown striking differences between African-American and Caucasian children in cotinine levels after exposure to tobacco smoke, but no studies have looked at differences using objective measures of nicotine in the air, they said.

For this study -- of 220 asthmatic children who had previously been part of the placebo-controlled Cincinnati Asthma Prevention trial -- the researchers used household air nicotine, rather than parents' reports, as the measure of exposure to smoke.

The nicotine levels over the year-long study were captured by dosimeters placed in the homes of participating children, who all had physician-diagnosed asthma, had symptoms consistent with persistent asthma, and were exposed to at least five cigarettes a day at home.

The study cohort was biracial, with 55% of the children -- ages five to 12 -- being African American.

"African-American children suffer from higher rates of tobacco-related disorders, such as asthma, sudden-infant death syndrome, and low birth weight, and we need to know why," Dr. Wilson said. "So our goal is to understand how certain populations -- particularly those groups who are most susceptible -- respond to (second-hand smoke) exposure."

Day-to-day levels of exposure were measured by serum samples of cotinine, which reflect exposure over the previous few days, while long-term exposure was measured by hair samples.

The study found:

• There were no significant differences in nicotine exposure between racial groups.
• Over time, African-American race was significantly associated with serum cotinine (P=0.0015) and with hair cotinine (P<0.0001) in a univariate analysis.
• The differences remained significant when covariates -- such as the size of family home -- were included.

The African-American children had higher serum and hair cotinine levels at all time points.

For example, in the 12-month analysis, the African-American children had 1.39 mcg/dL of cotinine in serum on average, compared with 0.80 for Caucasian children, a difference that was significant at P=0.001.

At the same time, their average hair cotinine was 0.28 nanograms per milligram, compared with 0.08, which was significant at P<0.0001.

Because higher levels of cotinine have been associated with increased school absences and the prevalence of asthma, the study has important implications, the researchers said.

"African-American children may handle environmental tobacco smoke differently than white children," Dr. Wilson said.

All the children in the study had asthma, which may limit how widely the findings apply, Dr. Wilson and colleagues noted. There was also no measure of how much second-hand smoke the children were exposed to outside the home.

"Exposure to tobacco smoke is dangerous for everyone, regardless of age or race," said Mark Rosen, M.D, president of the American College of Chest Physicians. "These findings underline the importance of eliminating environmental tobacco smoke in every setting, especially those where children are present."

The study was supported by the National Heart, Lung, and Blood Institute, the Robert Wood Johnson Generalist Physician Faculty Scholars Award, and the University of Cincinnati Department of Internal Medicine. The authors said they had no conflicts of interest.