My gfr number has decreased over the past 5 years, yet my bun and creat have been normal, is this calculated correctly?

Good question.: The estimated GFR commonly reported on lab results is calculated by a formula that tends to underestimate true kidney function, particularly the closer to normal the kidney function is. With a normal BUN and creatinine, there is probably little concern. If there is any question, though, a 24 hr urine creatinine clearance would be a better calculation of your kidney function. Hope this helps!