When a person uses tobacco, the addictive substance nicotine is rapidly absorbed into the bloodstream. The body quickly processes this compound, breaking it down into several byproducts, the most significant of which is cotinine. Health professionals and researchers measure cotinine to determine an individual’s level of tobacco exposure. This measurement is an objective way to quantify tobacco use, including exposure from a single cigarette.
Why Cotinine is the Preferred Biomarker
Cotinine is the preferred biomarker because it remains stable in the body much longer than nicotine itself. Nicotine has a very short half-life, reducing by half in approximately two hours, which makes it unsuitable for measuring anything but very recent use. This rapid clearance means that nicotine levels fluctuate dramatically throughout the day, providing only a snapshot of exposure.
The liver’s cytochrome P450 enzyme system, primarily CYP2A6, converts roughly 70 to 80 percent of absorbed nicotine into cotinine through oxidation. This metabolic conversion makes cotinine a stable indicator of exposure. Cotinine then circulates with a half-life ranging from 16 to 20 hours, sometimes extending up to 40 hours in certain individuals.
This extended half-life allows cotinine to accumulate to predictable levels, providing a reliable measure of chronic tobacco consumption or exposure from a single event. The concentration of cotinine is a more stable and accurate reflection of overall nicotine intake than measuring nicotine itself. Cotinine tests are widely used in clinical settings, public health research, and for insurance or employment screening.
Individual Variability in Cotinine Production
It is impossible to provide a single, fixed number for the amount of cotinine produced from one cigarette because numerous biological and behavioral factors influence the final concentration. The nicotine yield absorbed from a standard cigarette is estimated to be about 1 milligram, but the actual amount varies widely. Smoking topography, including the depth of inhalation, the frequency of puffs, and how much of the cigarette is smoked, directly impacts the quantity of nicotine absorbed.
Individual metabolic rates create the largest source of variation in cotinine production and clearance. Genetic differences in the CYP2A6 liver enzyme cause some people to be “fast metabolizers” who clear cotinine quickly, while others are “slow metabolizers” who retain it longer. These differences mean that two people who smoke the exact same cigarette may have vastly different cotinine levels. The ratio of cotinine to its secondary metabolite, trans-3′-hydroxycotinine, is often used to estimate an individual’s CYP2A6 enzyme activity.
Other physiological factors also contribute to this variability, including body mass, hydration status, and kidney function. For a person who does not regularly use tobacco, a single cigarette can result in a measurable increase in cotinine. Levels typically range from 50 to 200 nanograms per milliliter (ng/mL) in urine, 1 to 5 ng/mL in blood, and 2 to 10 ng/mL in saliva. This wide range reinforces why cotinine levels are always reported as concentrations or ranges, not as a precise amount linked to one cigarette.
Timeline for Detecting Cotinine in the Body
The detection window for cotinine depends on the biological fluid tested, as each fluid clears the metabolite at a different rate. Urine is often the most sensitive matrix for testing because cotinine concentrations are typically much higher than in blood or saliva. This higher concentration makes it easier to detect low-level exposure from a single cigarette.
After a single exposure, cotinine can be detected in blood and saliva for approximately one to three days. Saliva testing is non-invasive and provides results that correlate closely with blood levels, generally clearing from the oral fluid within one to four days. Urine offers the longest detection window for an isolated event, with cotinine remaining detectable for up to four days.
The effective timeline for a “positive” result is determined by the testing threshold, which is the minimum cotinine level required to register a positive result. Many laboratories use a threshold of 10 to 20 ng/mL for serum or plasma to distinguish smokers from non-smokers, while urine cutoffs are often set between 50 and 200 ng/mL. A single cigarette can easily push a non-smoker’s cotinine level past these thresholds. This makes a detectable result dependent on both the amount absorbed and the sensitivity of the specific test used.