What type of blood test is used to check for nicotine in the bloodstream? and how long is nicotine detectable in blood stream?

Nicotine: Either blood nicotine levels or its presence or absence can be determined. The length of time that nicotine stays in the body and that can be a reliable indicator of nicotine use, depends on the amount of tobacco smoked, the number of years smoking tobacco, and the type of nicotine test performed. It can be as short as 2 days, or as long as 3 months.

Nicotine & cotinine: Both how much and if it is present at all can be detected in the blood- either nicotine directly or one of its metabolites, cotinine, is detected and measured. Nicotine can be detected up to 3 days past the last use, sometimes longer depending on amount used and your health and age. Cotinine, however, can be detected up to 10 days past your last use. The standard test is actually a urine test.