Not of This Earth (1988)

Nadine is hired to be a live in nurse for Mr. Johnson, who has some sort of ailment that requires regular blood transfusions.  Johnson, a secretive man who always wears sunglasses, is an alien scout trying to determine if Earth is a good planet to take over.  He picks up hookers and sends their blood - or tries to send their bodies - back to his planet.  The aliens need blood to survive, hence his constant transfusions.

The opening credits include all sorts of monsters and death scenes that are not in the film, so don't get too excited.  It's just a jumble of scenes from other Roger Corman movies.  Traci Lords stars as the nurse and was better than I expected.