How long after quitting smoking will a blood test come back negative for nicotine?

Testing fluid: Usually urine and oral fluid are tested, rather than blood as the metabolite of nicotine is detectable in urine for a week after last exposure. Two weeks would be a safe time frame.

Poss 7 days: In a light smoker, on NO nicotine replacement therapy (no GUM, or patches), the half live on Cotinine, is only 20 hours, so neg in about 5 days. It will be higher therefore, last longer in a heavy smoker.