Cotinine in Blood: How Long Does It Stay Detectable?

Cotinine is a biomarker used to measure exposure to nicotine. It is a metabolite of nicotine that remains in the body for a longer period compared to nicotine itself.

How Long Does Cotinine Stay in Blood?

• Half-life: 16-20 hours
• Detectable for up to 2-3 weeks after last exposure
• Heavy smokers may have cotinine levels detectable for up to 4 weeks

| Blood Cotinine Level | Time After Last Exposure |
|---|---|---|
| Less than 10 ng/mL | 24 hours |
| 10-40 ng/mL | 2-3 days |
| 40-100 ng/mL | 1 week |
| Over 100 ng/mL | 2-3 weeks |

Factors Affecting Cotinine Clearance

• Metabolism: Individuals with faster metabolisms clear cotinine more quickly.
• Body weight: Cotinine is stored in body fat, so heavier individuals may have longer detection times.
• Smoking intensity: Heavier smokers have higher cotinine levels that take longer to clear.
• Quitting smoking: Cotinine levels typically drop rapidly after quitting, but can remain detectable for weeks.

Stories of Cotinine Detection

Case 1: Exposure Monitoring

• Benefit: Quantifying nicotine exposure to assess compliance with smoking cessation programs.
• How to: Collect blood samples and measure cotinine levels at regular intervals.

Case 2: Forensic Analysis

• Benefit: Determining smoking status in criminal investigations or child custody cases.
• How to: Interpret cotinine levels in conjunction with other evidence, such as witness testimony or physical examinations.

Case 3: Secondhand Smoke Exposure

• Benefit: Assessing the level of secondhand smoke exposure in nonsmokers.
• How to: Measure cotinine levels in blood or urine to estimate nicotine inhalation.