If it goes to a lab for extensive testing, they do more than just using instant test strips like in your home testing kit. These instant tyoe tests are popular with pobation officers and when they get a positive they will then send it out to a lab. Still they also make a instant strip that can test for validty just like the instant strip tests for the presence of drugs. If you went to someplace like Labcorp or Quest the sample is tested much more thoroughly (but not necessarily more sensitive or more accurate) than the stick test. It will go through validity testing to test pH, specific gravity, and possibly creatinine clearance. It will then go through an immunoassay test. Although not a dipstick, it uses the same technology as what makes the dipsticks work. Then if there is a positive presence of drug metabolites the sample is considered non-negative and confirmation is performed by GC/MS.

Those home tests are quite accurate, 95-98%. If you passed those you stand in good shape to pass unless you over diluted again.