Will Passive Inhalation of Marijuana Cause a False Positive?

I was just asked this question last week. The donor was at a party and other people were smoking marijuana, not the donor. The donor was afraid that they may have inhaled some of the smoke. It is very unlikely that an individual could inhale enough marijuana smoke to produce a positive drug test at the cut off levels currently observed by most drug testing laboratories. The Donor may have some trace of the drug in their system but not enough to register a positive at a cutoff level of 50ng/ml.
The National Institutes of Health conducted passive inhalation experiments in which subjects were exposed to the smoke from 16 marijuana cigarettes for one hour a day for nearly a week. Further the subjects were in unventilated rooms with the smoke blowing directly in their faces, so much so they supposedly required googles to protect their eyes. Only after this kind of extreme exposure did anyone produce a positive drug test equivalent to that of someone who had smoked just one marijuana cigarettes. In studies conducted under less extreme conditions no drug test were positive for more than a few hours after exposure and the measured cannabinoid levels were low.