See, that confounds me: I'd have expected "urine test" to be a perfectly reasonable way to put it, while "wee wee test" sounds infantilising. Latin- and Greek-derived words often do retain in English that aura of learning, though, given their mostly technical and literary use – I'm not referring here to old loans that have changed almost beyond recognition – so perhaps the doctor was just attempting to be friendly.
It goes the other way, too: I understand there are all sorts of everyday Turkish words which in Greek are associated with colloquial, regional or archaic expressions, and have often been considered the mark of an uneducated speaker in a country where the educational system tried for a long time to purify the national language and extirpate this kind of "foreign admixtures". Seeing haber ("news") on a Turkish television channel, for example, may seem amusing to a Greek, who is used to the lower register of phrases like "τι χαμπάρια;" και "δεν χαμπαριάζει καθόλου", as opposed to the more formal ειδήσεις.