Nicotine, or its primary metabolite cotinine, is most often tested to evaluate tobacco use.Long-term smoking of tobacco products can increase the risk of developing many diseases including lung cancer, COPD, stroke, heart disease, and respiratory infections. Long-term tobacco use can also exacerbate asthma and help promote blood clot formation. In pregnant women, smoking can impair growth of the developing baby and lead to low birth weight babies.

Because use of tobacco products can greatly affect the health of individuals, companies may use nicotine/cotinine testing to evaluate prospective employees for tobacco use. Many health and life insurance companies test applicants for nicotine or cotinine as well.

Nicotine and cotinine can both be measured qualitatively or quantitatively. Qualitative testing detects the presence or absence of the substances, while quantitative testing measures the concentration of the substance. Quantitative testing can help distinguish between active smokers, tobacco users who have recently quit, non-tobacco users who have been exposed to significant environmental tobacco smoke, and non-users who have not been exposed.

Cotinine may also be measured in saliva and in hair, although hair testing is primarily used in a research setting, such as a study of non-smokers exposure to tobacco smoke.

A blood or urine nicotine test may be ordered by itself or along with cotinine if a health practitioner suspects that someone is experiencing a nicotine overdose.

When a person has reported that he or she is using nicotine replacement products but is no longer smoking, nicotine, cotinine, and urine anabasine measurements may sometimes be ordered. Anabasine, an alkaloid, is present in tobacco but not in commercial nicotine replacement products. If a sample tests positive for anabasine, then the person is still using tobacco products.

Cotinine and/or nicotine testing may be ordered whenever an evaluation of tobacco use status or tobacco smoke exposure is required.

A court may order testing for child custody purposes. When a person enters a smoking cessation program, blood or urine cotinine tests may be ordered to evaluate his or her compliance. Urine, blood, or saliva testing may serve as a screen for tobacco use when someone is applying for life or health insurance. Since smoking can increase the risks of medical complications, testing may be performed prior to orthopedic, spinal fusion, wound revision, and plastic surgery as well as pulmonary therapy and organ transplantation.

Nicotine and cotinine are sometimes measured when someone has symptoms that a health practitioner suspects may be due to a nicotine overdose. Symptoms of mild nicotine poisoning may include:

• Nausea, vomiting
• Dizziness
• Drooling
• Weakness

More serious nicotine poisoning may result in:

• Increased blood pressure and/or heart rate, which suddenly drops
• Slowed or difficulty breathing
• Abdominal cramps
• Agitation, restlessness, or excitement
• Burning sensation in mouth
• Confusion
• Fainting
• Headache
• Muscular twitching
• Seizures, convulsions
• Coma

Hair testing is rarely performed in a clinical setting but may be ordered when an evaluation of longer-term tobacco use is desired.

In the blood, the nicotine level can rise within a few seconds of a puff on a cigarette. How much it rises depends on the amount of nicotine in the cigarette and the manner in which a person smokes, such as how deeply he or she inhales. The rate at which nicotine is metabolized and cotinine is cleared from the body also varies from person to person due to some genetic differences.  

When someone stops using tobacco and nicotine products, it can take more than two weeks for the blood level of cotinine to drop to the level that a non-tobacco user would have and several weeks more for the urine level to decrease to a very low concentration.

In general, a high level of nicotine or cotinine indicates active tobacco or nicotine replacement use. A moderate concentration indicates a tobacco user who has not had tobacco or nicotine for two to three weeks. A lower level may be found in a non-tobacco user who has been exposed to environmental smoke. Very low to non-detectible concentrations are found in non-tobacco users who have not been exposed to environmental smoke or in tobacco users who have refrained from tobacco and nicotine for several weeks.

When a nicotine overdose is self-evident, the person may not be tested for nicotine or cotinine.  The concentration would typically be increased, but the level does not necessarily correlate with the severity of a person's symptoms.

Test results based on different samples (blood, urine, saliva) are not interchangeable.

Some pesticides contain high concentrations of nicotine.This can be another source of nicotine poisoning. In fact, nicotine is itself a pesticide sometimes used in "organic" farming as an alternative to organophosphate or pyrethrinoid derivatives.

Nicotine is found not just in the tobacco plant but also in other plants in the same family. These include potatoes, tomatoes, eggplants, and red peppers. The concentration of nicotine in these plants, however, is much lower than that in tobacco. The cutoffs of the nicotine/cotinine tests have been set to discriminate dietary sources of nicotine from tobacco use and second-hand smoking.

A person's genetic makeup may influence how they metabolize nicotine.Variations in the genes that code for the CYP2A6 and CYP2B6 liver enzymes affect the rate of nicotine metabolism. (For more on this, see our article on Pharmacogenetic Tests.)