For medical, legal or insurance purposes, it is sometimes necessary to measure a person's nicotine levels. This can be done reliably through urinalysis or blood testing. Blood tests are not uniformly successful or accurate, but they can give a general picture of whether or not the person has recently used a tobacco product.
Nicotine and Cotinine
When nicotine is absorbed into the body, it breaks down into cotinine. A blood test for nicotine will usually include a measurement of cotinine levels.
Half-Life
Nicotine has a half-life of roughly two hours, meaning that half the nicotine in the body converts to cotinine every two hours. Cotinine's half-life is roughly twenty hours.
Time Frame
Because nicotine is metabolized so quickly, a blood test will only detect trace amounts after 24 to 72 hours. Cotinine may take up to 10 days to drop to levels undetectable by blood test.
False Negatives
Blood test results may fail to detect nicotine if the blood sample more than 24 hours after the person last smoked or chewed tobacco.
False Positives
People with certain types of liver defect may show nicotine and cotinine in their blood weeks or months after quitting.
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