I personally have mine tested yearly, does throw the new receptionists, as there isnt a 'true' reason for doing it, but it is peace of mind for me, and bearing in mind that htey can lose up to 75% of kidney and liver function before you would notice, I like to know what their results are, they can then be compared each year. If you know the results while they are healthy, it does help, as sometimes cats can be in teh normal range but still need meds, as the normal range might be different for them. Good luck!!