The estimated glomerular filtration rate (eGFR) is widely used as a surrogate marker of renal function and is mathematically derived from the patient's serum creatinine, using their age, sex and ethnicity. There is some controversy over whether ethnicity should be included in the calculations.
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Calculation
The eGFR can be calculated using a number of different formulas including the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and the Modification of Diet in Renal Disease (4-v MDRD). 4-v MDRD is arguably the most used and is calculated using a four variables formula:
eGFR (mL/min/1.73m2) = 186 (serum creatinine in µmol/L × 0.011312)-1.154 × (age)-0.203 × (0.742 if female) × (1.212 if African/American Black)
Prior to the introduction of this formula, eGFR derivation required an accurate body weight, which was a significant impediment to its easy adoption into routine clinical practice.
Since 2021 there has been a new CKD-EPI equation that functions without using ethnicity or race 2.
Glomerular filtration rate
The actual glomerular filtration rate (GFR), as opposed to the estimated GFR, is of course more accurate but is much more laborious to measure, with methods including:
-
inulin clearance
inulin, a polysaccharide, is completely filtered at the glomerulus with no tubular secretion or reabsorption
not to be confused with insulin despite very similar spelling
Therefore in routine clinical practice, the eGFR is the usual test of renal function.
Limitations
The published literature advises caution in the use of the MDRD (modification of diet in renal disease) calculation in:
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any condition where body weight may markedly differ from that theoretically expected from age and sex:
See also
Not to be confused with
EGFR - (capital E) a similar abbreviation for - epidermal growth factor receptor (EGFR) mutation