FBR Cotinine FAQ

What's the advantage of using cotinine measurements when I can rely on patients telling whether they've quit or not?

Most patients may try to be truthful when answering questions about their smoking behavior. Self-reporting can be unreliable, however; consciously or unconsciously patients may temper their responses to please their doctor. More importantly, it's not only how many cigarettes are smoked, but also the nicotine content of the cigarettes smoked, and how they're smoked. Two individuals may each have cut down to "half a pack" a day, but one may have switched to a higher tar, unfiltered product which is inhaled more fully, and the second may switch to a lower tar cigarette which is occasionally puffed. These two "half a pack" a day smokers would be exposed to much different levels of cigarette smoke, discernible only by an objective standard such as cotinine.

The figure on the right demonstrates the wide variability in cotinine levels associated with self-reported smoking. This helps to explain why self-reported smoking cannot be used reliably to measure actual exposure to inhaled cigarette smoke.

Cotinine has an in vivo half life of about 24 hours. Nicotine's half-life is about 30 minutes. Timing of sampling relative to the last cigarette smoked may account for some fluctuation of cotinine levels in steady smokers. For smokers with a fairly constant smoking pattern, cotinine levels reach a steady state, varying only by 15%-20% over the course of the day. Levels should be lowest in the morning as there is typically minimal exposure to cigarette smoke overnight. Once a sample is collected, metabolism ceases and cotinine levels should not change; however, saliva or urine left at room temperature for extended periods may experience degradation of cotinine due to bacterial contamination.

What assay does FBR use, and how does FBR assure the quality of its cotinine assay?

The cotinine assay is a double antibody competitive inhibition radioimmunoassay, developed here at FBR. Monitoring includes the use of control samples placed at the beginning, middle, and end of each assay. Control levels are compared within and between assays in order to detect any drift or assay errors, should they occur. If control values are outside of acceptable levels, the results from that run are discarded, the error identified and corrected, and the samples re-assayed. Additionally, urine specimens are serially diluted in order to assure that an accurate value is obtained from the optimum part of the assay's curve.

Serum is the specimen of choice for cotinine measurement since it is subject neither to bacterial degradation nor sample concentration. Cotinine can also be measured in saliva in concentrations similar to those in serum; however sample collection is cumbersome as is sample extraction. Most cotinine is excreted by the kidneys into the urine, where it is concentrated about 10X higher than it is circulation. This makes it the specimen of choice for determination of passive exposure. Urine, while easy to collect from children, is subject to contamination and should be kept cold prior to shipping. FBR's assay can reliably detect cotinine levels consistent with passive (second-hand smoke) exposure in serum and urine.

Can serum and urine be used interchangeably to monitor smoking cessation efforts?

Since cotinine levels in urine are approximately 10 times higher than those is serum, both types of specimens can be used interchangeably as long as the practitioner remembers to account for the concentration in urine. However, if serial monitoring is desired, it is preferable to utilize only one specimen type.

Cotinine levels <10 ng/mL are considered to be consistent with no active smoking. Values of 10 ng/mL to 100 ng/mL are associated with light smoking or moderate passive exposure, and levels above 300 ng/mL are seen in heavy smokers - more than 20 cigarettes a day. In urine, values between 11 ng/mL and 30 ng/mL may be associated with light smoking or passive exposure, and levels in active smokers typically reach 500 ng/mL or more.

What's the best way to use urinary cotinine levels to monitor smoking cessation efforts?

The sensitivity of urinary cotinine measurements is ideal for monitoring smoking cessation efforts, especially if the FBR is informed of the perceived smoking behavior of the patient. This will allow the appropriate dilution to be used, thus improving turn around time. If possible, collect the urine samples at approximately the same time of day to reduce diurnal variation. Determination of the creatinine level for each urine sample as a measurement of dilution will help the user to establish cotinine trend among serial samples.

FBR's cotinine report suggests that my patient may be a light smoker, but he swears that he doesn't smoke. What explanation might account for this discrepancy?

Assuming that the patient is being truthful, your patient could be exposed to cigarette smoke on the job, at home, or elsewhere. Second hand smoke can be responsible for relatively high cotinine levels; patients should be advised to reduce their exposure to second hand smoke.

Cotinine is a metabolic byproduct of nicotine. Nicotine replacement medications produce cotinine just as tobacco does. FBR should be advised if nicotine is available to the patient in pharmacological form.

My pregnant patient doesn't want to quit smoking because she doesn't want another 12 pound baby. What can I tell her?

While the association between low birthweight and easy delivery may invite continued cigarette usage during pregnancy, pregnant patients should be cautioned that low birthweight is also associated with increased likelihood of neonatal intensive care admission. In turn, this is usually associated with increased hospital stay (delaying time to return home) increased expenses, and of course, increased sickness and risk of death for the infant.

Can cotinine levels be used reliably in custody cases, i.e., if a parent seeks evidence that when in the custody of an ex-spouse a child is exposed to dangerous levels of cigarette smoke?

FBR discourages the inappropriate dependence on cotinine levels in this type of scenario. While the biochemical measurements are accurate, they must be regarded only as one piece of evidence. Cotinine levels may reflect cigarette exposure, but may not be useful in determining responsibility.

Smoking has long been recognized as a predictor of extended recovery time for certain surgical procedures. You may wish to determine if patients undergoing elective surgery are currently smoking in order to predict the success of procedure. Postponement of elective procedures until cotinine levels are in the non-smoking range may be considered.