I recently took a home drug test in which the cut off level is 50ng it came up negative rather quickly. But I have read that most pre employment test cut off at 15ng.
Only the confirmation GC/MS test has a 15 ng cutoff threshold. An initial Immunoassay screen is performed first and most I/A's have a 50 ng threshold - the same as the home assays.

But dont let the differing cutoffs worry you. Even though their cutoffs numerically differ, a 50 ng assay screen is functionally eqiuivalent to the 15 ng GC/MS. For more info, do an Advanced Search with the terms "functionally equivalent metabolites".

If your home tests are consistently negative with the first urination of the day (regardless of line intensity), youre good to go.