Andrea, I think a 18 hour post test won't be effective. The NCD stays in the body for 4-7 hours. If you stop the NCD and do the test 24 hours later. No NCD will be in your body anymore and excretion will not increase.

I would try the following protocol(without the vitamin C to make sure that you do not take a chelating agent):

http://kitty98004.tripod.com/wwwncdheavymetalstestcom/toxic_heavy_metals_testc.html

or visit

http://ncdtest.com

Hope this helps.