Serum Cotinine Level

Environmental tobacco smoke (ETS) contains a mixture of toxic chemicals, including known human carcinogens. The U.S. Surgeon General has concluded that ETS causes a range of adverse health outcomes in adults, ranging from nasal irritation to increased risk of coronary heart disease to lung cancer. In children, the Surgeon General has concluded that ETS causes lower respiratory illnesses, adverse effects on lung function, onset of wheezing, asthma, middle ear disease, and Sudden Infant Death Syndrome (HHS, 2006). Household ETS exposure is an important issue because many people, especially young children, spend much time inside their homes. Infants and younger children are more susceptible and vulnerable to the effects of ETS than are older children because they are still developing physically, have higher breathing rates than adults, and have little control over their indoor environments (HHS, 2006; U.S. EPA, 2011).

Exposure to ETS leaves traces of specific chemicals in people's serum, urine, saliva, and hair. Cotinine is a chemical that forms inside the body following exposure to nicotine, an ingredient in all tobacco products and a component of ETS. Following nicotine exposures, cotinine can usually be detected in serum for at least 1 or 2 days (Pirkle et al., 1996). Active smokers almost always have serum cotinine levels higher than 10 nanograms per milliliter (ng/mL), while non-smokers exposed to low levels of ETS typically have serum concentrations less than 1 ng/mL. Following heavy exposure to ETS, non-smokers can have serum cotinine levels between 1 and 10 ng/mL (CDC, 2009, 2015a).

The purpose of this indicator is to track exposure to ETS, or secondhand smoke, among the non-smoking U.S. population. Cotinine is considered the best biomarker for tracking exposure among non-smokers to ETS. Accordingly, this indicator reflects serum cotinine concentrations in ng/mL among non-smokers for a representative sample of the U.S. population, age 3 years and older, as measured in the 1988-1994, 1999-2000, 2001-2002, 2003-2004, 2005-2006, 2007-2008, 2009-2010, and 2011-2012 National Health and Nutrition Examination Survey (NHANES). NHANES is a series of surveys conducted by the Centers for Disease Control and Prevention's (CDC's) National Center for Health Statistics, designed to collect data on the health and nutritional status of the civilian, non-institutionalized U.S. population using a complex, stratified, multistage, probability-cluster design. Serum cotinine also was monitored in non-smokers age 4 years and older as part of NHANES III, between 1988 and 1994. CDC's National Center for Environmental Health conducted the laboratory analyses for the biomonitoring samples. Beginning in 1999, NHANES became a continuous and annual national survey. Continuous NHANES does not include cotinine data for children from birth to 3 years of age, the group reported to be the most vulnerable to the effects of ETS.

The results of NHANES III (1988-1994) and continuous NHANES (1999-2012) are presented here for the different survey periods by sex (Exhibit 1), race and ethnicity (Exhibit 2), and age (Exhibit 3). During the 1988-1994 survey period, the median serum cotinine level (50^th percentile) among non-smokers in the general U.S. population was 0.176 ng/mL. In 1999-2000, the estimated median serum (50^th percentile) cotinine level among non-smokers nationwide had decreased to 0.060 ng/mL. During the most recent survey period (2011-2012), the estimated median serum cotinine level for the U.S. population was 0.020 ng/mL (see Exhibit 1). This marks a greater than 65 percent decrease from levels measured in 1999-2000 and a nearly 90 percent decline since NHANES III (1988-1994)—a consistent reduction over time that suggests a marked decrease in exposure to ETS. Similar decreasing trends in serum cotinine levels are observed between NHANES III (1988-1994) and the most recent 2011-2012 survey across sex, race/ethnicity, and age groups (CDC, 2014). However, CDC reports that 40.6 percent of children age 3 to 11 years still had detectable cotinine in their serum in 2011-2012 (CDC, 2015a).

These data reveal three additional observations: (1) non-smoking males have slightly higher cotinine levels than females across survey periods (Exhibit 1); (2) of the ethnic groups presented, non-Hispanic blacks had the highest cotinine levels (Exhibit 2); and (3) in general, people below the age of 20 have higher serum cotinine levels than people age 20 years and older (Exhibit 3).

Exhibit 4 shows the percentage of children between the ages of 3 and 17 with specified serum cotinine levels, for the total age group and by selected race and ethnicity breakdowns. Among the three subgroup populations presented, Mexican American children had the lowest percentage of serum cotinine levels greater than 1.0 ng/mL; this was evident for all time periods displayed. Between 1988-1994 and 1999-2000, black, non-Hispanic children had the largest absolute decline in the percentage of serum cotinine levels greater than 1.0 ng/mL, but that population also started off with the highest percentage above 1.0 ng/mL (33.7 percent). In 2011-2012, the percent of children with serum cotinine levels greater than 1.0 ng/mL decreased by 6.2, 3.5, and 11.8 percent among non-Hispanic blacks, Mexican Americans, and non-Hispanic whites, respectively, compared to 1999-2000.

• The relatively small number of samples collected in a two-year cycle (e.g., 1999-2000 or 2001-2002) may, in some cases, result in measures of central tendency that are unstable from one survey period to the next.

Continuous NHANES (1999-2012) data used for Exhibits 1 through 3 of this indicator were obtained directly from CDC's Fourth National Report on Human Exposure to Environmental Chemicals, Updated Tables, August 2014 (CDC, 2014a). NHANES III (1988-1994) data for Exhibits 1 through 4 were generated with Stata statistical software using NHANES laboratory data files available online (CDC 2014b, 2015b). Continuous NHANES (1999-2012) data used for Exhibit 4 also were generated with Stata statistical software using NHANES data files available online in SAS^® transport file format (CDC, 2015b).