What is eGFR and what to do about results
What is eGFR?
eGFR - stands for estimated Glomerular Filtration Rate, which is a
derived value from serum creatinine, age, sex, and race. It is an estimate of kidney function. The laboratory eGFR is not corrected for race currently. (x1.21 if Afro-caribbean) The 95% confidence intervals for the eGFR values are quite large (about +/- 30%) e.g. eGFR for a 60 yr old male with creatinine of 150 would be 44 (95% confidence limits 31 to 57). The trend of eGFR is important.
Normal value approx 100 ml/min
Values of eGFR are placed in stages of Chronic Kidney Disease (CKD) 1 to 5
What are the stages of CKD?
When to measure the eGFR
At presentation and then at least annually in :
- Heart failure
- Vascular disease - coronary, cerebral and peripheral
- Any kidney disease or significant bladder problem
- Multisystem disease - rheumatoid arthritis
- Potentially nephrotoxic drugs - ACEIs, ARBs, NSAIDs, Lithium
I have an eGFR result - what should I do now?
Caution about eGFR Estimation
It is only an estimate. A significant error is possible. eGFR is most likely to be inaccurate in people at extremes of body type, for example malnourished, amputees, etc. - but see Race, below.
Confidence intervals: 90% confidence intervals are quite wide, e.g. 90% of patients will have a measured GFR within 30% of their estimated GFR. 98% have measured values within 50% of the estimated value. For an individual patient values will be much more consistent than this, just as creatinine values are - e.g. a 20% fall in eGFR is certain to reflect an important change.
Race: Some racial minorities may not fit the equation well. It was originally validated for US white and black patients. For Afro Caribbean black patients, eGFR was 21% higher for any given creatinine. So if race was not included in the estimate you have, it should be increased by approx. 20% for a black patient. In the UK white population, and probably in South Asians living in the UK, the equation seems to work quite well. It may not perform so well in all racial groups.
Not so good near normal: The equation tends to underestimate normal or near-normal function, so slightly low values should not be over-interpreted.
Creatinine level must be stable: eGFR calculations assume that the level of creatinine in the blood is stable over days or longer. They are not valid if it is changing.
Age: The equation is not valid for under-18s.
eGFR is estimated GFR calculated by the abbreviated MDRD equation :
175 x (Creat / 88.4)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if black)
Download eGFR tables