As a matter of fact it will let you know when you close to the cutoff and sending the vial in for further testing is essential to know exactly where you stand
This is incorrect. Home tests (as well as the assays used by the labs for the initial screening) are a "Pass/Fail" endeavor only. They have no ability to give a quantitative value. And without a quantitative value, you will not know how close you are to the assays cutoff threshold. All that you will know is that youve either passed or failed.

And the urine testing methodologies used by the labs are not all that sophisticated as they are portrayed to be. The lab will perform an Immunoassay for the initial screen (which functions on the same principle as the home assays, and is a PASS/FAIL endeavor only). If the sample fails the I/A screen, the sample is sent to the GC/MS for confirmation (with a cutoff threshold of 15 ng/ml) and with this methodology, a quantitative value is provided.