One thing that slightly bothers me Burnt, is that while I agree it's almost impossible to find actual web evidence of someone failing a test in the US by subbing besides it being outside temp., dirty or dilute, and that it is illegal to test for hormone levels, your statement, and that by others, that they ONLY test for banned substances is patently false.
Ive never made such a statement - youve got me mistook for someone else. If you do any digging of my previous posts, Ive stated time and time again that specimen integrity checks have become SOP in recent years.

And again, they dont compare samples because, like Ive stated, constituent levels will vary from sample to sample. A persons sample whos had unsatisfactory creatinine & S/G can, days later, submit another sample with satisfactory creatinine and S/G -
that is providing that the donor had learned his/her lesson of not going overboard on the fluid intake.

And labs practicing in the US are prohibited from performing any type of genetic testing on samples collected for an employment-related drug test unless permission is granted by the donor on an entirely seperate and detailed consent form. Such donors are protected from genetic profiling under the Genetic Information Nondiscrimination Act (GINA), which was revised and signed into law in 2008 by then-President George W. Bush.
Even if genetic profiling laws were never put into place, genetic testing is very costly and complicated in process. With that being stated, if employers were really out to catch cheaters, it would be more economically feasible to the bean counters to utilize alternative testing methods, such as hair testing.

Finally, to answer your question as to a retest being observed due to dilution, Under DHHS regulations (as well as DOT regulations), an observed recollect is warranted if the creatinine level is between 2 - 5 mg/dL. It has been determined that while its physiologically possible for a donor to submit a sample with such a low creatinine level, such cases are extremely rare. Therefore, an observed collection is warranted to rule out the possibility of a donor attempting to submit a "non-human" urine sample.