Just to relate a recent experience regarding egfr. The purpose is to hopefully reduced a lot of the worry and/or panic many post about when there is a sudden change in their egfr.
I am a person with one kidney. A person with one kidney MAY maintain what is classified as a normal egfr. BUT in most cases there will be an increase in Creatinine level which results in a lower egfr. It is quite normal for a person with one kidney to have a Creatinine level of 1.8 mg/dl (159 umol/l). In my case over the past two, three years since kidney removal my Creatinine level has been about 1.7 quite consistently. I get tested every 3 weeks as I am receiving cancer treatment for kidney cancer that has spread to the bone (that is why kidney was removed it was cancerous).
My past three tests (over 9 or 10 week period went up to 1.8 and remained there). As we age (I am close to 72) kidney function normally declines so this was not surprising, but none of us likes to see the number increase and worry about why.
My last visit to the cancer doctor my Creatinine was again 1.8 (159) resulting in an egfr of 40. This was at 8:30 am on that day. The very next morning, at about the same time of day my kidney doctor did a renal blood test (which includes Creatinine and egfr) and it was 1.5 with egfr of 49. So in 24 hours I went from egfr of 40 to 49. after many weeks of being consistently egfr of 39, 40.
I fully anticipate going back to the 1.8 level. But the point is if you get a sudden higher Creatinine level, thus lower egfr, don't panic, try not to worry. It can vary significantly as was my experience in just 24 hours. Simply give yourself time, get retested, and monitor you level on average over time. It is not an exact science. You can get a test which is suddenly above or below your typical but then on the next test return to what is your true norm.
Low EGFR
Lupus nephritis 
