Answer:
in our urine there is protein, when the test solutions are applied, it causes a break down of the protein and that's when it reads pos. or neg. if there is that certain protein in your system. So I would like to add, there are certain tests/testing methods that are use by certain gov. agencies that no matter what you use to clean/flush your system, you can't bet it. ie; when you" flush" your system, you also get rid of any and all of your protein and to some testers, that's as good as a dirty test. Get it?