Not necessarily. Various stores carry products designed to defeat these tests. If I were you, I'd check with "tobacco and smoking accessory" shops in your area. Another source is health food stores. One particular health food store that I know of has a closet behind the register where they keep a product called "naturally clean" herbal tea. You make 2 gallons of this tea, drink it continuously for 8 hours before the test, 30 min before the test you would take something to make your urine dark yellow and a couple of creatine capsules. Works like a charm.
Call around and ask for a tea that rids your body of toxins. The ones that know what you're talking will have it. The ones that don't are strike outs.
Otherwise, drink lots of fluid between now and then. To the point of feeling water logged. Make sure that you "go" at least a few times before your appt. and that you will be able to go again when necessary.
Good luck.