Need help creating a loop

Hi i need help creating a loop function and i was hopeing some nice ppl in here could help me.

What i need is a loop that looks thru the raid to see how many got a certain buff
but i only want it to return if the person also got hp below lets say 90
and then I want to use the return to cast a spell.
lets say 5 ppl got the buff and are below 90 hp i want to cast a spell.

Is this possible?