Estimated glomerular filtration rate (eGFR), CKD-EPI

Estimated glomerular filtration rate (eGFR) is a calculated indicator of kidney function that reflects the kidneys’ ability to filter blood. The result is expressed in ml/min/1.73 m² and is used for the evaluation, staging, and monitoring of chronic kidney disease (CKD).

In the laboratory, eGFR is calculated based on serum creatinine using the modern validated CKD-EPI Creatinine Equation 2021 formula. The formula takes into account serum creatinine, age, and sex and does not include a race variable.

eGFR is considered more informative than an isolated creatinine value because serum creatinine levels are influenced not only by kidney function, but also by muscle mass, age, sex, diet, and certain medications.

eGFR determination is used for:

• assessment of overall kidney function;
• identification of patients at risk for chronic kidney disease;
• staging and monitoring of chronic kidney disease;
• assessment of renal and cardiovascular risk;
• monitoring kidney function in chronic diseases;
• dose adjustment of renally excreted medications;
• evaluation of kidney function before administration of contrast agents or nephrotoxic drugs.

For comprehensive kidney assessment, eGFR interpretation is recommended together with albuminuria testing or urine albumin-to-creatinine ratio (ACR).

Components

• Serum creatinine - the primary biochemical marker used for eGFR calculation
• Patient age - included in the formula because glomerular filtration rate physiologically declines with age
• Patient sex - used to account for physiological differences in creatinine production
• CKD-EPI Creatinine Equation 2021 - a modern validated calculation formula for adult patients without the use of a race coefficient

Indications

The test is recommended in cases of:

• suspected chronic kidney disease;
• diabetes mellitus;
• arterial hypertension;
• cardiovascular disease;
• family history of kidney disease;
• albuminuria, proteinuria, or persistent hematuria;
• follow-up after acute kidney injury;
• prescription of medications with renal elimination;
• assessment of kidney function before contrast-enhanced procedures;
• monitoring elderly patients and patients with chronic comorbidities.

Limitations and interpretation considerations

The CKD-EPI Creatinine Equation 2021 formula is validated for adult patients and should be interpreted cautiously in situations where creatinine levels may not accurately reflect true kidney function:

• significantly increased muscle mass;
• reduced muscle mass, sarcopenia, or cachexia;
• severe obesity;
• malnutrition;
• strict vegetarian diet or excessive meat consumption before testing;
• use of creatine supplements;
• pregnancy;
• unstable kidney function or suspected acute kidney injury.

Special pediatric formulas are used for patients under 18 years of age.

Procedure

Venous blood is collected for testing. Serum creatinine is measured using a standardized laboratory method, after which eGFR is automatically calculated using the CKD-EPI Creatinine Equation 2021 formula.

Sources:

https://www.kidney.org/kidney-topics/estimated-glomerular-filtration-rate-egfr
https://www.kidney-international.org/article/%2520S0085-2538%2823%2900766-4/fulltext?utm
https://www.kidneyfund.org/all-about-kidneys/tests/blood-test-egfr
https://reference.medscape.com/calculator/251/egfr-using-ckd-epi-2021-update