Nicotine Exposure and Metabolites

Nicotine is an addictive substance found in tobacco products and is one of the most heavily used addictive drugs in the United States. Use of tobacco products, particularly smoking, is the main preventable cause of disease and death in the U.S. Active smoking is also recognized as a risk factor for poor wound healing in postoperative outcomes studies. The main metabolites of nicotine are cotinine, trans-3'-hydroxycotinine, and nornicotine; of these, cotinine is the most widely used marker for detecting nicotine exposure. Laboratory testing of urine for nicotine and its metabolites can help differentiate between active and passive nicotine exposure based on the concentrations detected; however, these results are not definitive. Nicotine replacement therapy and tobacco use can be distinguished by the detection of a tobacco-specific alkaloid, such as anabasine. Testing of plasma or serum, when necessary, is useful for identifying recent exposure.

Quick Answers for Clinicians

What is the cutoff for cotinine to distinguish smokers from nonsmokers?

In ARUP Laboratories tests, the cotinine concentration in serum or plasma that is used as a cutoff to distinguish smokers from nonsmokers is 10 ng/mL. In urine, the concentration of cotinine to distinguish smokers from nonsmokers is 100 ng/mL, although active smokers routinely have a cotinine concentration that exceeds 1,000 ng/mL. The positive cutoff for passive exposure is 2 ng/mL in serum and 20 ng/mL in urine.

What is the window of detection for nicotine and its metabolites?

The window of detection for nicotine is brief; therefore, nicotine concentration may not be a good indicator of smoking status. However, cotinine, a major metabolite of nicotine, may be detected up to 7 days after exposure. Tobacco users who abstain from tobacco for 2 weeks have cotinine concentrations comparable to those of unexposed nontobacco users, <3 ng/mL. However, due to potential secondary or tertiary exposure, one can present with persistently low concentrations of cotinine in urine even after smoking cessation.

How is anabasine testing used to determine smoking status?

Anabasine is a minor tobacco alkaloid that can be used as a biomarker to evaluate smoking abstinence and can help differentiate between individuals using tobacco and those using various nicotine replacement therapies. However, anabasine testing has a relatively low clinical sensitivity, and anabasine may be present in supplements and electronic cigarettes. Because of the possibility of false-positive and false-negative results, anabasine levels should be interpreted in the context of other nicotine biomarkers. A study from ARUP Laboratories has shown that anabasine can be present in concentrations of up to 144 ng/mL in urine samples of individuals who test positive for nicotine.

Does laboratory testing for exposure differ based on the nicotine delivery source?

Although the uptake of nicotine differs among delivery sources, and electronic cigarettes, nicotine gum, and nicotine patches all deliver less nicotine than traditional cigarettes, clinical laboratory testing for exposure is the same, regardless of the delivery source.

Can certain foods lead to a positive test for nicotine or metabolites?

Dietary intake of nicotine may be an important factor in the interpretation of nicotine testing in nonsmokers. Foods that contain nicotine include cauliflower, eggplants, potatoes, and tomatoes. An individual may consume enough of these foods to obtain 1 µg of nicotine, the amount comparable to that inhaled by a passive smoker. The method of absorption is different when eating than it is when inhaling, and the level of nicotine is lower when the nicotine-containing foods are cooked.

Indications for Testing

Testing is appropriate when it is necessary to evaluate individuals for recent use of nicotine-containing products or passive exposure to nicotine. Testing can also be used to document use of tobacco versus purified nicotine products to assess compliance with smoking-cessation programs or to verify abstinence from nicotine-containing products when qualifying patients for surgery or organ transplant.

Laboratory Testing

Quantitative Testing

Urine

Urine testing is recommended to detect chronic use because analytes are detectable for a longer period of time in urine than in serum or plasma. The trans-3'-hydroxycotinine metabolite may persist in urine for weeks after cessation of long-term or heavy use of nicotine products. Urine metabolite testing is also recommended to determine active or passive exposure, although testing cannot differentiate the two definitively. Anabasine, a tobacco alkaloid, can also be detected in urine and may distinguish the active use of tobacco products from use of nicotine replacement therapy; individuals using purified nicotine products would not be expected to have anabasine in urine. Because nicotine can be found in varying amounts in several foods, including cauliflower, eggplant, tomatoes, and potatoes, and in some teas, consumption of such foods may explain the presence of nicotine and its metabolite cotinine in the urine of nonsmokers. A cotinine cutoff of 100 ng/mL is frequently used for surgery qualification purposes.

Serum or Plasma

Serum or plasma testing may be required when a valid urine specimen cannot be obtained, for example, from anuretic patients or those on dialysis. Serum or plasma testing can detect recent use, typically within the past 2 weeks, and the results correlate more closely with results of oral fluid testing than urine testing. Serum or plasma testing by quantitative liquid chromatography-tandem mass spectrometry cannot distinguish between use of tobacco and purified nicotine products. A cotinine cutoff of 10 ng/mL is frequently used for surgery qualification purposes. See also the Emergency Toxicology topic.

Qualitative Screening

The cotinine qualitative screen is recommended to assess active exposure to nicotine and to document abstinence from nicotine-containing products for compliance with smoking-cessation programs or for surgery qualification. Those who do not use tobacco may test positive for cotinine because of passive exposure to cigarette smoke. When assessing tobacco use using a qualitative screen, a higher cutoff value may produce false-negative results, whereas a lower cutoff value may produce false-positive results due to passive exposure. Additionally, because of variations in the metabolism of nicotine, ideal cutoff values may be specific to gender and ethnicity. Quantitative urine testing is preferred to determine passive use or differentiate between tobacco use and nicotine replacement therapy.