Some Google research and I learned a few interesting things about this particular test.
Urine is the preferred medium to test, because Cotinine is concentrated about 10X higher in urine than in circulation.
Passive exposure (second hand smoke) can lead to levels as high as 30ng/ml in urine, which is consistent with levels of light smokers. The FBR website specifically states that there is no determining line between a light smoker and someone who is exposed to secondhand smoke in sufficient quantities.
Sounds like you were hanging out at the local dive bar last week a few times.
