WHY DO DOCTORS SAY STAT?
'Stat' in doctor lingo means 'immediately!'. "Stat" is derived from the Latin word 'statum' meaning 'right away'.
Doctors write stat on prescriptions when they want their orders filled right away. For example, in hospital, medicines are typically dispensed at predetermined scheduled times to patients. If I need a medicine delivered to a patient urgently then instead of just entering the order into a prescription log book I will also write stat next to it to alert nurses that this is a request that requires emergent action.
This also works on Pharmacy prescriptions. For example, after dropping off a prescription you typically wait half an hour to an hour for the pharmacist to put your order together. But if for example, you had a migraine and I wanted you to immediately have a medication wafer for relief I would write the order for take home meds and for one dose to be given stat. This alerts the pharmacist that you need an immediate fill of one of the tablets on the spot and the remainder can be filled at their leisure.
In my medical experience I've come across the use of stat way more on written requests than verbal. That's because for example in an ER, saying 'stat' it is pretty much redundant as the staff you're working with already know that what you're asking for is urgent. So now you know. Go read some more of my articles stat :-)