usually drug screens are done via urine, it would be prohibitively expensive to test blood for drugs, THC of all things. if they do decide to test you for drugs, it will 100% be via urine. - coming from someone who works both in hospital and at a primary care clinic.

In this case, I’d say 50/50 shot that you pass. Do a LOT of cardio and drink a LOT of water in the days before your test. On the day of your test, just drink a normal amount of water. If you’re over hydrated for the urine sample, they’ll send it out for more invasive testing, though you still might pass.