How To Tell If you Need A New Filter For Air Purifier?

Hey guys, I was a Honeywell Air Purifier 52 500 some time ago a friend. I do not know how it was used or if the filter or pre-filter was replaced, because his parents sent him there donna.Y but I can not tell whether it needs a new filter or a new filter? Together they cost about $ 100, so I prefer not to simply for the pleasure of buying faire.Merci!