Estimated glomerular filtration rate

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.

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:

• Cr-51 labelled ethylenediaminetetraacetic acid (EDTA)
• Tc-99m labelled diethylenetriaminepenta-acetic acid (DTPA)
• I-125-iothalamate
• 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
• creatinine clearance

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:

• acute renal failure
• any condition where body weight may markedly differ from that theoretically expected from age and sex:
  • pregnancy
  • anasarca
  • sarcopenia
  • amputeeslimb amputation
  • paraplegicsparaplegia
  • morbid obesity
  • malnutrition

See also

Not to be confused with

• EGFR - (capital E) a similar abbreviation for - Epidermalepidermal growth factor receptor (EGFR) mutation