saliva testing?

ok well my wife has to do one of these but she hasn't smoked in like 2 to 3 weeks and she still positive. She took one of those at home urine test. So my question is when they use this mouth swab test will it tell or not? cause I read in a couple threads that say the saliva test only goes back as much as 72 hours is this true? Help!!!!:D

ANYONE?:confused:

naw dude its straight saliva tests are 24 hour, piss tests are like a month or 2.. your wifes completely legit dont even worry about it

Sweet Thanks.