Blood tests used for screening tobacco exposure do not primarily look for nicotine. Nicotine is rapidly broken down in the body, limiting its usefulness as a long-term indicator of exposure. A blood sample is preferred over other biological materials for definitive proof of tobacco or nicotine use due to its stability and ability to provide highly quantitative results.
The Primary Target: Cotinine
Blood tests focus on cotinine rather than nicotine due to differences in how the body processes each compound. Nicotine is quickly metabolized by the liver, mainly by the enzyme CYP2A6, into its major breakdown product, cotinine. Nicotine has a very short half-life in the bloodstream, typically only about one to four hours.
Cotinine is far more stable and reliable as a biomarker because it has a much longer half-life, averaging around 16 to 20 hours. This extended presence allows cotinine to remain detectable in the blood for several days, providing a wider window of detection for recent nicotine use. Approximately 70% to 80% of absorbed nicotine is converted into cotinine, making its concentration a direct reflection of intake.
The presence of cotinine indicates exposure from any source, including traditional cigarettes, e-cigarettes, cigars, pipes, or nicotine replacement therapies like patches and gums. The detected level is proportional to the degree of exposure, allowing facilities to distinguish between light use, heavy use, and passive exposure. Since cotinine is only produced when nicotine is processed, its detection provides objective evidence that nicotine has entered the system.
Laboratory Methods for Blood Analysis
Blood tests for cotinine rely on specialized laboratory techniques to identify the compound and precisely measure its concentration. The two main categories of analysis are initial screening and confirmatory testing. Initial screening often employs Immunoassay (IA), a rapid, cost-effective technique used for high-volume testing.
The Immunoassay works by using antibodies designed to bind specifically to the cotinine molecule in the blood sample. When cotinine is present, the antibodies attach, triggering a measurable reaction, typically a color change or a fluorescent signal. While IA is fast and sensitive, it can sometimes produce false-positive results if the antibodies cross-react with other compounds, such as other nicotine metabolites.
For definitive results, particularly when legal or financial consequences are involved, the confirmatory test is Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). This two-step process first uses liquid chromatography to physically separate cotinine from all other components in the blood sample. Next, the separated cotinine molecules enter the mass spectrometer, which acts as a molecular fingerprinting tool. The mass spectrometer ionizes the cotinine and measures its precise mass and fragmentation pattern, confirming its identity and providing an exact quantitative measurement.
Detection Windows and Concentration Levels
The time cotinine remains detectable, known as the detection window, is significantly longer than nicotine and is influenced by its half-life. While nicotine is typically cleared within one to three days, cotinine can be detected in the bloodstream for up to a week following the last use. The exact time frame is highly variable, depending on individual factors such as genetics, hydration levels, kidney function, and the frequency and intensity of nicotine use.
Testing facilities use specific concentration thresholds, measured in nanograms per milliliter (ng/mL), to categorize the level of exposure. A typical cutoff for serum cotinine to distinguish a non-user from a user is set between 10 ng/mL and 15 ng/mL. Non-users who report no secondhand smoke exposure generally have levels below 1 ng/mL, while minor passive exposure may raise levels up to 5 ng/mL.
Active, regular smokers typically exhibit substantially higher cotinine concentrations, often ranging between 250 ng/mL and 350 ng/mL, and sometimes reaching 800 ng/mL in heavy users. These quantitative levels allow laboratories to differentiate accurately between a daily smoker, a light or intermittent user, and someone who has only experienced environmental secondhand smoke exposure. Individual differences in CYP2A6 enzyme activity can impact how quickly nicotine is converted and cleared, affecting the final concentration reading.
When and Why Blood Nicotine Tests Are Used
Blood cotinine testing is utilized when a high degree of precision and objective evidence of nicotine exposure is necessary. One common application is in the health and life insurance industry, where underwriters use the quantitative results to assess health risks and determine premium rates for applicants. The test provides reliable verification of self-reported smoking status.
Another major use is pre-surgical screening, where medical teams confirm a patient’s abstinence from smoking. Nicotine exposure can significantly impair wound healing and increase the risk of complications during and after surgery, making verified non-smoking status an important safety measure. Blood cotinine tests are also employed in clinical settings to monitor compliance in smoking cessation programs, providing an objective measure of adherence.
The tests are also used to assess environmental exposure, such as evaluating the risk to children or pregnant women from secondhand smoke, which requires the low-level quantification capabilities of blood analysis. When definitive, verifiable evidence of recent exposure and accurate quantification is required for administrative or legal purposes, testing the blood for cotinine remains the preferred method.