Also, I call bullshit on the unable to test for gender in the piss test. As far as I've always learned, when studying biology, was the hormones and other markers in the urine are gender specific.
I've never tested this knowledge to be positive, but I'll take the information given to me by professors and people who have been through med. school over a poorly constructed article with glaringly apparent errors.
I would hypothesize that basic level drug tests don't test gender, but not that tests are unable to determine gender. Although, its common knowledge that many people try to pass drug tests with other people's pee, so I would think they would specifically test for gender unless its extremely costly.
I've never failed a test after being well hydrated and having clear urine. Your urine is supposed to be almost clear unless you're dehydrated.