@teachaero From experience I know that lab values can show "wonky" [My favorite word today!] values at times. What you have been eating or not eating, your hydration levels at time of the test, even the time of day labs are pulled, can affect the results. A good Dr will look at the values over a range of time. And, I second what @maxwell123 and @kamama94 say about kidney function having a natural decrease as we mature into senior years, and a kidney disease will hasten the decrease in function. Have the Dr's given you any indication for the reason for decline?
Ginger