First, I just want to say that I realize that any line, however faint it is, is supposed to be construed as a negative. Having said that, is there a particular reason why one person's urine would show up as a faint line, whereas other's would show up a clear, solid line? I have taken several different types of home tests. On the ones I have passed, the line is always VERY faint. Some are fainter than others. Sometimes I have to struggle to make out the pinkish line, but it is indeed there. Using these same home tests, I've tested my wife's urine who I know is 100% clean, as well as some Quick Fix urine. Those lines are always clear, dark red. Background on me - I've been clean for 2 weeks. Heavy smoker before that. I'm surprised that I'm showing up negative on some of these tests anyways, though I have a fast metabolism and am very thin. So basically, what does a faint line signify? If it has nothing to do with THC levels, what causes one to be faint and another to be solid?