GFR-vs-eGFR.txt  11/12/2022

GFR is Glomerular Filtration Rate and it is a key indicator of renal function.

eGFR is estimated GFR and is a mathematically derived entity based on a
patient's serum creatinine level, age, sex and race
<b>https://ukkidney.org/health-professionals/information-resources/uk-eckd-guide/about-egfr</b>

GFR is Glomerular Filtration Rate and it is a key indicator of renal function

eGFR is estimated GFR and is a mathematically derived entity based on a
patient’s serum creatinine level, age, sex and race. This is usually calculated
by the laboratory analysing the blood sample and reported along with the
serum creatinine result. A number of recognised and well-validated formulae
have been used for this purpose including the MDRD and CKD-EPI equations.

“Normal” GFR is usually >90 ml/min/1.73m2. (Note the correction for body surface
area “per 1.73m2” which is important for certain patient groups, e.g. amputees,
extremes of body habitus.) It is best to follow the locally calculated eGFR if
possible although one can be calculated using an eGFR calculator.

 It is important to bear in mind the following pitfalls and cautions when interpreting the eGFR:

    It is only an estimate of kidney function and a significant error is possible. 
    The eGFR is most likely to be inaccurate in people at extremes of body type e.g.
    patients with limb amputations, severely malnourished and morbidly obese individuals

    Confidence intervals: The 90% confidence intervals are quite wide, e.g. 90% of patients
    will have a true GFR within 30% of their estimated GFR and 98% have measured values
    within 50% of the estimated value.

    For an individual patient, however, serial values will be much more consistent than this
    just as creatinine values are – e.g. a 20% fall in a patient’s eGFR is certain to reflect
    an important change.

    Look at the trend in eGFR – Identifying trends in eGFR is often more informative than
    one-off readings. i.e. a progressive fall in eGFR across serial measurements is more
    concerning than stable readings which don’t change over time.

    Race: There is increasing concern that the adjustment for ethnicity does not reflect
    the wide diversity within individuals of black ethnicity, with the adjustment based
    on outdated and unfounded biological assumptions for differences between ethnic groups
    at the expense of better understanding of social and ancestral determinants.

    In the 2021 NICE chronic kidney disease (CKD) guideline the recommendation to adjust
    for ethnicity, present in the 2014 version, has been removed. On review of the evidence,
    NICE agree that adjusting for ethnicity when calculating eGFR may not be valid or accurate.

    The UKKA supports NICE and recommends that the adjustment for black ethnicity for eGFR
    be removed from UK practice. Further evidence is needed and there is concern by
    professionals and patients that adjustment may be a source of inaccuracy and potential inequity.

    Not so good near normal: The equations used for estimating eGFR tend to underestimate normal
    or near-normal function therefore slightly low values (i.e. around the 60 ml/min/1.73m2
    CKD “cut-off” level) should not be over-interpreted.

    In this situation repeat testing, looking for a progressive decline in renal function
    over time, or measurement of cystatin C (a different biomarker of kidney function) may
    be useful. Additional indicators or renal disease should also be sought in these patients
     – e.g. urinalysis looking for blood and protein, positive family history of renal disease etc…

    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.

    Values can differ between laboratories. Creatinine measurements can differ significantly
    between laboratories depending on the methods used to measure it. Furthermore, different
    laboratories may use a different formula to calculate the eGFR further complicating
    comparison of eGFR measurements obtained from different laboratories.

    Creatinine level must be stable: eGFR calculations assume that the level of creatinine
    in the blood is stable over days or longer i.e. steady-state; they are not valid if it
    is changing. It is therefore not valid in patients with acute kidney injury or in
    patients receiving dialysis, for example.
    Age: MDRD and CKD-EPI equations are not valid for individuals under 18 years of age.

http://www.woodsmall.com/GFR-vs-eGFR.txt    c2022