High Serum Creatinine/ Low eGFR

I am very healthy female age 46.  I am 5'6" and weigh 130 lbs and work out at least 3 mornings a week.  I have never had body fat tested but assume I am pretty lean.  I have low bp and take no meds.  Annual physical just came back.  I have borderline high cholesterol at 202 with LDL at 125.  This has been my range for the last 5 years as previously physician always ran cholesterol.   However, my Serum Creatinine is 2.08 (.57-1.00); my Glom Filt Rate is 26 (greater than 59); my Bun/Creatinine Ratio is 6 (8 - 27).  Physician says maybe I was dehydrated and wait until after first of year to recheck.  

What can cause these labs?  What do you suggest?  

[elin]

want to know should I be concerned twice in 3 months my eGFR was 57 all other in normal range