Initially blood drawn every 2 weeks- was able to get down to once a month and prn with any symptoms. My veins are paying the price. It is esp important to stay on top of renal function with urine tests and BUN and Creat testing. It seems that it depends on your sx, meds and medical team. Never hesitate to request lab work if you are concerned and have sx - plus with the meds we take it is vital to stay on top of things.