Hello,

Sorry for an obvious question, but are you using the same creatinine value for both calculations? In other words, the eGFR from your lab uses a creatinine value. Did you use the same value when checking with the NKF calculator? If so, there are different calculators used for GFR such as:

CKD-EPI Creatinine 2009 Equation (Preferred method)
MDRD Study Equation
CKD-EPI Creatinine 2012 Equation
Cockcroft-Gault Formula
Revised Bedside Schwartz Formula (For ages 1-17)

All have their own merits and limitations but to be honest the variation is small and likely not clinically meaningful. Furthermore, we don't truly know which calculator is the most accurate as each might be more accurate in some populations versus others. Therefore, if your eGFR is 52 versus 57 does not really matter. Instead, I would choose one calculator (such as the MDRD eGFR we use on UKidney (found here) and then monitor your own trend. Trends over time using the same method are more meaningful than small absolute differences at any point in time.

Dr. Jordan Weinstein