Quote Originally Posted by Burnt Toast
Instant drug tests do not read "negative" or "positive", so therefore its impossible for a drug test resulting in neither positive nor negative for THC.

What likely happened was the tech saw a faint line, and either s/he wasnt sure how to interpret it, or s/he flat out misinterpreted the faint line as a "positive" and sent the sample out for a confirmation test. Either way, the sample would be confirmed negative for THC.

Bad synthetic batches are distinguished by the dissipitation of the urine constituent "buffers" (particularly creatinine and SG) that are tested during the validity check.

Another thing: having THC residue on your hands have no effect on any urine test. Urine tests check for drug metabolites and not residues. Therefore, the THC must be ingested and metabolized into THCA before it becomes detectable on the U/A.
I guess I missed the part about the test being instant, thanks for straightening this out BT.