I wish I could offer some advice. Both of my cats are young, Corkscrew is 3 and Tibby is 2. I've had bloodwork drawn on Corkscrew once when he was sick, but so far I haven't needed to with Tibby. I do think that when they older I would like to get it done one a year, but I guess it would also depend on how healthy they were and how well they reacted to the stress of getting it done.