The CKD eGuide is derived from the NICE, SIGN, and Renal Association guidelines.
eGFR is estimated Glomerular Filtration Rate, usually based on serum Creatinine level, age, sex, and race. The most widely used method for this is the abbreviated MDRD equation, as it has proved the most robust and accurate (see further info at foot of page). Normal GFR is approximately 100mls/min/1.73m2. Use locally calculated eGFR if you have one, but to calculate eGFR approximately you can use our eGFR calculator
If you already know the GFR, you can click below for info on different GFR levels:
It is important to note the following Important cautions about eGFR
- 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. See Race, below. It is not valid in pregnant women or in children (see Age, 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 groups may not fit the MDRD 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 in the MDRD study. 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 the equation seems to work quite well. It may not perform so well in all racial groups.
- Not so good near normal: The MDRD equation tends to underestimate normal or near-normal function, so slightly low values should not be over-interpreted. Furthermore, laboratory differences in creatinine estimations may make significant differences. Routine reporting of eGFR values >90 is not recommended and many labs are now reporting all values over 60 as >60. Note however that a significant (e.g. 20%) rise in creatinine while eGFR is >60 may still be important as it will usually reflect a real change in GFR.
- 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 MDRD equation is not valid for under-18s. Use the Counahan-Barrat method for children - e.g. the paediatric calculator from Steve Fadem at nephron.com
- Which MDRD equation? in the UK, most laboratories calculate eGFR on all samples sent for creatinine measurement. Since 2006 the equation they use should take into account local variations in accuracy of creatinine assays, so eGFR values obtained in this way should be a little more accurate than those generated by any of the online calculators (including ours). Technically, this is the "175" equation used with a correction factor when necessary, rather than the original "186" equation.
Information about these tests for patients
The level of creatinine in the blood is a useful guide to kidney function, but GFR (glomerular filtration rate) is a more accurate measure. Blood creatinine can be used to estimate GFR (eGFR) using age, sex, and race, and this is often calculated by computer and reported along with the creatinine blood test. If it isn't but you know the creatinine result, you can use our eGFR calculator
Normal GFR is approximately 100mls/min/1.73m2 but you will often see it reported as >90 ("more than 90") or >60.
The kidneys filter approximately 100mls/min, or 150 litres per day. Of that 100mls/min, 99mls is reabsorbed in the nephron, so that only about 1ml/min finally passes into urine. Further information about blood tests and kidney function from the Edinburgh Renal Unit website.
GFR is used to measure the severity of kidney damage. Because it is normally about 100 it gives an approximate "% kidney function". The K/DOQI CKD stages distinguish 5 grades of severity which can be useful in planning management. Stages of CKD.
The eGuide home page has downloadable information leaflets and further links.