From site: The object of the game is to score as many points as possible by matching the appropriate blood type of a donor to the blood type of a recipient. During each round, a total of 10 recipients will walk onto the screen. You then click on the donor you think is a match — there’s no guarantee that a match exists every time. Each round has a set amount of matches you must make to proceed, and time gets shorter with each progressive round you face.
The hardest part of the game is knowing what donor blood types match. You may also have a chart of blood type matches available while you play.