Nicotine is the active compound in tobacco and vaping products, a naturally occurring alkaloid that affects the central nervous system. When consumed, it is rapidly absorbed into the bloodstream and metabolized. Blood tests are a highly accurate method used by medical professionals, researchers, and insurance companies to determine an individual’s exposure. While nicotine can be detected in blood, the compound itself is short-lived. Detection relies on the body’s metabolic processes, focusing on breakdown products rather than the presence of the original compound alone.
The Primary Target: Cotinine
Nicotine is quickly metabolized by the liver, meaning the active substance remains in the bloodstream for only a short period. The half-life of nicotine is typically around two hours. This rapid clearance makes testing for nicotine itself unreliable for determining anything other than very recent use. The body converts the majority of absorbed nicotine into a substance called cotinine.
Cotinine is the main metabolite of nicotine and serves as the preferred biomarker for nicotine exposure because of its stability. This molecule has a significantly longer half-life than its parent compound, generally ranging from 16 to 20 hours, though sometimes up to 40 hours. This extended presence allows testing to detect nicotine use that occurred days earlier, providing a much more accurate picture of a person’s status. The concentration of cotinine in the blood plasma is directly proportional to the amount of nicotine consumed, establishing it as the reliable standard for determining exposure levels.
Detection Windows in Blood
Blood testing is a highly specific and accurate method for determining recent nicotine exposure, often using chromatography-mass spectrometry to measure concentrations precisely. Nicotine itself can be detected in the blood plasma for a relatively brief period, usually disappearing within one to three days after the last use. Its rapid breakdown means that a blood test for nicotine alone would likely yield a negative result shortly after use.
The presence of cotinine extends the window of detection significantly, providing a much wider timeframe for accurate screening. Cotinine typically remains detectable in blood plasma for up to ten days after the last nicotine exposure. Because of its longer half-life, cotinine levels decrease slowly enough that a single blood draw can confirm usage that occurred over a week earlier. Blood tests are frequently employed for high-stakes purposes such as health insurance underwriting due to their precision in measuring the exact concentration of cotinine.
Individual Factors Affecting Clearance
The detection window is not a fixed period, as several biological variables influence how quickly cotinine is cleared from the system. One major determinant is the frequency and intensity of use. A heavy user will accumulate higher baseline concentrations of cotinine that take longer to fall below the detection threshold. Conversely, an intermittent or light user will clear the metabolite much faster. The liver, which is the primary site of metabolism, plays a significant role in this clearance process.
The efficiency of nicotine and cotinine metabolism is largely controlled by the cytochrome P450 enzyme CYP2A6. This enzyme converts over 70% of nicotine to cotinine and is exclusively responsible for the subsequent metabolism of cotinine. Genetic variations, known as polymorphisms, in the gene that codes for CYP2A6 can result in individuals being slow, normal, or rapid metabolizers. Individuals with reduced-function CYP2A6 variants clear cotinine more slowly, which can prolong their detection window.
Interpreting Test Results
A blood test result for nicotine exposure is interpreted against established “cut-off levels” or testing thresholds. These thresholds are the minimum concentrations required to register a positive result. Cut-off values are not universal and can range from 10 to 20 nanograms per milliliter (ng/mL) in serum, depending on the purpose of the test. A result above the cut-off is considered positive, indicating recent exposure.
The measured concentration of cotinine helps to differentiate between levels of exposure, not just a simple positive or negative. Levels below 10 ng/mL in serum often suggest passive exposure to secondhand smoke, or a person who quit recently. Concentrations between 10 ng/mL and 100 ng/mL may indicate light or intermittent use. Levels significantly above 100 ng/mL are typically associated with regular, heavy nicotine use. The interpretation relies heavily on the context of the testing, as an insurance company may use a very low cut-off to identify any nicotine use, whereas a clinical cessation program may use a higher threshold to confirm abstinence.