Cotinine is a chemical substance produced in the body when nicotine is broken down. Its presence serves as a reliable indicator of recent nicotine exposure, primarily from tobacco products like cigarettes, cigars, smokeless tobacco, or nicotine replacement therapies.
Cotinine as a Biomarker
Nicotine itself has a short half-life, meaning it is quickly processed and eliminated from the body, typically within about two hours. This rapid clearance makes nicotine less suitable for assessing ongoing or recent exposure over extended periods. Cotinine, conversely, is a metabolite of nicotine with a much longer half-life, generally ranging from 16 to 40 hours, making it a more stable and dependable indicator of nicotine exposure over the past few days.
Cotinine’s extended presence in the body allows for a wider detection window, providing a clearer picture of an individual’s exposure. It remains detectable in various biological samples for several days, sometimes up to a week, after nicotine use. The stability of cotinine in samples like blood, saliva, and urine enhances its utility as a biomarker for tobacco smoke exposure, including passive or secondhand smoke.
Methods for Measuring Cotinine
Cotinine levels can be measured using various biological samples, each offering specific advantages regarding detection windows and ease of collection. Urine testing is a common method, as cotinine concentrations are higher in urine than in blood or saliva, making it suitable for detecting exposure over the past few days. Urine samples are also easy to collect.
Blood tests provide highly accurate measurements of cotinine and reflect recent exposure. Saliva testing offers a non-invasive alternative with results that correlate well with blood levels, providing a detection window similar to blood and urine. Hair follicle testing can detect nicotine exposure over a longer period, ranging from weeks to several months, but it is a less common and more expensive method.
These measurement techniques, such as high-performance liquid chromatography (HPLC), gas chromatography (GC), and mass spectrometry (MS), allow for precise quantification of cotinine in different samples. While some methods are more sensitive or cost-effective, the choice often depends on the required detection window and the specific context of the testing.
Interpreting Cotinine Levels
Interpreting cotinine levels involves understanding typical ranges that correspond to different levels of nicotine exposure, measured in nanograms per milliliter (ng/mL). Individuals with no active smoking or nicotine exposure have very low or undetectable cotinine levels, often less than 1 ng/mL in blood or saliva. It is uncommon for non-smokers in the U.S. to have levels exceeding 1 ng/mL.
People exposed to secondhand smoke may have detectable, but low, cotinine levels, often ranging from 1 to 10 ng/mL in blood, or up to 30 ng/mL in saliva. Levels in this range indicate passive exposure, and there can be some overlap between heavy passive exposure and light active smoking. For light or occasional smokers, or those using nicotine replacement therapies, cotinine levels fall into a moderate range, such as 10 to 100 ng/mL.
Active smokers exhibit high cotinine levels, exceeding 100 ng/mL in blood or saliva, and often much higher, potentially over 500 ng/mL or even up to 1000 ng/mL in urine. These distinct ranges help differentiate between active tobacco use, exposure to environmental tobacco smoke, and no significant nicotine exposure.
Factors Affecting Cotinine Levels and Clearance
Several factors can influence an individual’s cotinine levels and how quickly it is eliminated from the body, beyond the direct amount of nicotine exposure. An individual’s metabolism plays a role; genetic variations can affect the activity of enzymes responsible for converting nicotine to cotinine and then clearing cotinine from the system. This can lead to differences in cotinine accumulation for the same amount of tobacco exposure.
Liver function is important, as the liver is the main organ for metabolizing nicotine and cotinine. Impaired liver function can slow down this process, leading to cotinine remaining in the body for a longer duration. Age can affect metabolic rates, causing variations in cotinine clearance. Certain medications might interfere with the body’s ability to metabolize or excrete nicotine and cotinine.
The body’s hydration status and kidney function impact how quickly cotinine is excreted through urine. Cotinine levels peak after exposure and then gradually decline over time, with its half-life of approximately 16 to 20 hours meaning it generally takes about 8 to 9 days for the substance to be fully cleared from the system. The intensity and duration of exposure, the nicotine content of the product, and environmental factors like room ventilation influence the measured cotinine levels.