I also work in healthcare.
Being a female you are in a better position to substitute with clean natural male urine. You had better know this person extremely well though to avoid the possibility of any pharmaceuticals that they may take from causing a positive for something other than THC... Unless you are also prescribed something in the same drug class and able to verify (that is more complicated when it comes to opiods).
As a male, I am NOT in as good of a position to substitute with natural female urine. This usually only comes into play at or immediately following menstruation. In your case, during a drug screen collection they will not ask your last menstrual period. However, if I were to substitute with natural female urine which was collected at or around that time it would be highly unusual to detect that level of blood in male urine - especially when you can differentiate between hemolyzed and non-hemolyzed blood. They also do not ask your gender on the chain-of-custody form, but it is easy to determine gender based on name unless you have an unusual or foreign name. An example is that my girlfriend currently has her period - not a good idea to use her urine right now... Also my sister-in-law is currently pregnant mid-term. Her urine is totally clean. However, being that I am male it would also be unwise to use a pregnant female's urine which it would be possible to detect beta-hCG in.
So yes - substituting for a male's natural urine which you know to be totally clean is a possibility. Now you just have to figure out who, and also figure out your method of delivery (remember - nothing in your pockets. Crotch it somehow) as well as how to guarantee the temperature range by the time you hand the specimen cup over. Needs to be 92-98 F. If it reads 100 F you can always quietly blow on the specimen to cool it slightly before opening the door. Remember in an unobserved drug screen you typically have a maximum of 5 minutes to do what you have to do and produce the sample.
I should also add that as part of my job I have conducted drug screens (as a collector) for several years. I have conducted observed screens (ex: physicians for state med. board), DOT screens and collection protocols, and your run-of-the-mill non-DOT unobserved screens. Yours will be non-DOT, and I'm sure an unobserved collection for pre-employment (THC cutoff 50ng). Keep in mind many hospital systems have also started testing for nicotine in urine drug screen collections (this may affect your insurance, or even them hiring you). Keep this in mind if trying to find suitable urine to substitute. Nowadays for healthcare purposes this person should also be a non-smoker/non-vaper to avoid nicotine detection...
Anyway I hope this helps!
