The amount of nicotine, cotinine, carbon monoxide, or other components found in the body varies with the amount of tobacco used, the type of product used, and a person’s smoking behavior (e.g., how deeply the person inhales). However, within 3 to 4 days of quitting, any by-products found in the body should be at levels low enough to indicate that the person is no longer actively smoking.

Measuring concentrations of nicotine or its breakdown products (e.g., cotinine) in body fluids such as blood, urine, or saliva can reveal whether a person currently smokes and about how much the person smokes. Other tests for tobacco use measure concentrations of carbon monoxide or other gases in a person’s breath.

People exposed to secondhand smoke may have a measurable level of nicotine or nicotine by-products in their bodies, but the level is the result of passive inhalation rather than active tobacco use. If you are scheduled for testing, you may want to avoid closed areas where people are smoking for a day or two before the test is given.