Urine Cotinine

You can lie to a questionnaire. You cannot lie to your urine. Cotinine is the chemical your liver produces when it breaks down nicotine, and measuring it tells you whether nicotine has actually entered your body in the past few days, regardless of what you remember, admit, or notice.

That matters for two kinds of people. The first is anyone trying to verify their own quit attempt or confirm a partner, child, or housemate is genuinely smoke-free. The second is anyone who lives or works around smokers and wants to know how much nicotine they are absorbing without choosing to.

What This Test Actually Measures

Cotinine is the main breakdown product of nicotine. After you inhale nicotine from a cigarette, vape, secondhand smoke, or smokeless tobacco, your liver converts most of it to cotinine using an enzyme called CYP2A6. About 15 percent of nicotine leaves your body unchanged in urine. The rest is metabolized, with cotinine and its further breakdown products excreted over the following days.

Urine cotinine reflects two things at once: how much nicotine you have been exposed to recently (typically the past 2 to 4 days) and how quickly your body clears it. People with faster CYP2A6 activity will produce and excrete cotinine differently than people with slower activity, which is why interpreting a single number requires context.

Why You Should Care About Your Number

Higher urine cotinine tracks closely with greater nicotine intake, and that intake links to several concrete health outcomes in human studies. The clearest signals come from cancer, reproductive health, and heart and kidney disease.

Lung Cancer Risk

In a long-running study of Chinese smokers, urinary cotinine measured years before any cancer diagnosis predicted who later developed lung cancer. Smokers in the highest quartile of urinary or serum cotinine had roughly 5 to 6 times the odds of lung cancer compared with smokers in the lowest quartile. Adding cotinine to a model based on smoking history alone meaningfully improved how well the model identified people at risk, suggesting that cotinine captures exposure information that self-reported pack-years miss.

What this means for you: if you smoke and your cotinine is high, that number is not just confirming what you already know. It is identifying you as someone whose exposure level falls into the group with the highest measured cancer risk in prospective research, and who has the most to gain from cessation and from imaging-based lung cancer screening.

Heart Disease, Atrial Fibrillation, and Hypertension

In the PREVEND prospective cohort of about 4,700 adults, urine cotinine showed a graded relationship with cardiovascular disease, with risk rising as cotinine rose. A separate analysis from the same cohort found that both light and heavy current smoking, when assessed by urine cotinine, were associated with a higher risk of developing high blood pressure.

Secondhand exposure shows up here too. In the Multi-Ethnic Study of Atherosclerosis, never-smokers with greater secondhand smoke exposure (measured by urine cotinine) had about 1.6 times the risk of developing atrial fibrillation compared with those with the least exposure. The same cohort linked secondhand exposure to roughly 40 to 50 percent higher risk of heart failure events.

Kidney Function

Urine cotinine has a specific advantage in kidney research: it predicts incident chronic kidney disease independently of standard markers like albumin in the urine, while self-reported smoking does not. In a Korean middle-aged and older cohort, cotinine-verified current smoking was associated with moderately increased albuminuria across age, sex, body weight, and comorbidity strata. The implication is that cotinine catches people whose kidneys are absorbing real damage from smoke that they may be under-reporting on questionnaires.

Type 2 Diabetes

In the same PREVEND cohort, urine cotinine-assessed smoking status was a stronger predictor of type 2 diabetes than self-reported smoking. Adding cotinine improved diabetes risk prediction beyond standard factors like body weight, family history, and blood sugar.

Reproductive Health in Women

A study of 11,944 women across U.S. and Korean cohorts found a roughly linear dose-response between cotinine levels and shorter reproductive lifespan, with stronger effects at higher exposure. Higher cotinine was associated with earlier menopause.

Liver and Adolescent Health

In a U.S. study of 1,433 adolescents, serum cotinine was positively associated with liver stiffness (a proxy for early scarring) but not with hepatic fat. The signal here is that nicotine exposure may contribute to early liver injury independent of fatty liver disease, even in young people.

Why Urine Cotinine Beats Just Asking About Smoking

In an urban U.S. public hospital, routine cotinine screening found that 32 percent of self-reported nonsmokers actually had significant nicotine exposure. Among bladder cancer patients undergoing surveillance, self-reported smoking exposure was often inaccurate. People underestimate, forget, or hide their exposure, and they almost always underestimate how much secondhand smoke reaches them at home, at work, or in cars. Cotinine resolves the ambiguity.

Reference Ranges

Urine cotinine does not have a single universally accepted cutpoint. Optimal thresholds for distinguishing smokers from non-smokers vary by population, sex, and ethnicity, and they have shifted downward over time as background secondhand smoke has dropped. The numbers below come from large population studies and are illustrative orientation rather than universal targets. Your lab may report different units or use a different reference.

Source: PATH Study (Edwards et al. 2021), Ware et al. 2019, Le et al. 2026, Silva et al. 2021. Optimal cutpoints for non-Hispanic Black adults tend to run higher than those for non-Hispanic White or Mexican American adults, reflecting differences in nicotine metabolism rates. Lower-level secondhand smoke exposure in non-smokers can produce values well below these smoker cutoffs but still above zero.

What this means for you: the practical interpretation is simpler than the cutpoints suggest. If you have not used any nicotine product or been around smoke and your cotinine is undetectable, that confirms zero exposure. If you have any detectable cotinine, nicotine is reaching your body from somewhere, and the higher the number, the heavier the exposure. Compare your results within the same lab over time for the most meaningful trend.

When Results Can Be Misleading

A single urine cotinine reading reflects the past 2 to 4 days, so it can be distorted by short-term factors that have nothing to do with your typical exposure.

• Recent secondhand exposure: spending an evening in a smoky bar, sharing a car ride with a smoker, or visiting a household where someone smokes can produce a positive reading even if you do not use nicotine yourself.
• Nicotine replacement products: patches, gum, lozenges, and prescription nicotine products all contain nicotine and will raise your cotinine. The test cannot distinguish between cotinine from a cigarette and cotinine from a quit-aid product.
• Vaping and smokeless tobacco: e-cigarettes, nicotine pouches, and chewing tobacco all produce cotinine. A high cotinine reading does not, by itself, prove combusted cigarette use.
• Hydration and urine concentration: very dilute or very concentrated urine can shift the raw number. Reports that include creatinine adjustment correct for this; raw cotinine without creatinine adjustment is more variable.

Genetic variation in the CYP2A6 enzyme also affects how quickly people clear nicotine, which is one reason optimal cutpoints differ across ethnic groups. Two people with identical exposure can produce different cotinine numbers based on metabolism alone.

Tracking Your Trend

A single cotinine reading is a snapshot. The most useful information comes from tracking the trend, especially during a quit attempt or when you are working to reduce secondhand exposure at home or work.

A reasonable cadence: get a baseline before any change, retest 2 to 4 weeks after quitting or removing an exposure source to confirm the drop, then retest again at 3 months to confirm you have stayed off. After that, annual testing is enough for most people who want ongoing verification, with more frequent testing if you are at high relapse risk or if your home environment changes.

Because cotinine reflects only the past few days, a low or zero result confirms recent abstinence but does not prove you have been off nicotine for months. If you need to document longer-term abstinence (for example, before elective surgery), repeated testing over weeks is more reliable than one reading.

What to Do With an Unexpected Result

If you are a self-reported non-smoker and your cotinine comes back positive, the most likely explanations are secondhand smoke at home, work, or in a vehicle, or nicotine in a product you did not realize contained it. Audit your environment first. Retest after 1 to 2 weeks of strict avoidance to confirm the level drops.

If you are working to quit and your cotinine remains high after several weeks of attempted abstinence, that is a signal to escalate your strategy. Combination behavioral counseling plus pharmacotherapy (nicotine replacement, varenicline, or bupropion) has the strongest evidence for sustained quitting. A high cotinine after a quit date is not a moral failure; it is information that the current approach is not strong enough.

If your cotinine is high and you have any of the conditions linked to nicotine exposure (cardiovascular risk, kidney disease, family history of lung cancer, or trying to conceive), use the result as a prompt to discuss formal cessation support and, where appropriate, screening tests like low-dose CT for lung cancer in high-risk smokers.