88.9
mL/min/1.73m²
89
mL/min/1.73m²
2
0
88.9
mL/min/1.73m²
89
mL/min/1.73m²
2
0
The eGFR Calculator implements the CKD-EPI 2021 equation, the current gold standard for estimating glomerular filtration rate in adults. This updated equation was developed by the Chronic Kidney Disease Epidemiology Collaboration and endorsed by the National Kidney Foundation (NKF) and American Society of Nephrology (ASN) joint task force. The 2021 equation is a race-free formula that uses only serum creatinine, age, and sex as variables, replacing the 2009 CKD-EPI equation that included a race coefficient.
Glomerular filtration rate (GFR) is the single best overall index of kidney function in health and disease. It represents the volume of plasma filtered by the glomeruli per unit time, normally approximately 120 mL/min/1.73 m2 in young healthy adults. Direct GFR measurement requires clearance studies using exogenous markers such as inulin, iothalamate, or iohexol, which are impractical for routine clinical use. Estimated GFR based on serum creatinine provides a convenient surrogate that enables screening, diagnosis, and monitoring of chronic kidney disease across large populations.
The CKD-EPI 2021 equation takes the form: eGFR = 142 x min(Scr/kappa, 1)^alpha x max(Scr/kappa, 1)^(-1.200) x 0.9938^age x (1.012 if female), where kappa is 0.7 for females and 0.9 for males, and alpha is -0.241 for females and -0.302 for males. This two-slope spline function provides better accuracy than older equations across the full range of GFR values, with less bias at higher GFR levels compared to the MDRD equation. The removal of the race coefficient was based on evidence that race is a social rather than biological construct and that its inclusion could perpetuate health disparities.
Chronic kidney disease is classified into stages based on GFR: G1 (GFR 90 or above, normal or high), G2 (60-89, mildly decreased), G3a (45-59, mild to moderate decrease), G3b (30-44, moderate to severe decrease), G4 (15-29, severely decreased), and G5 (below 15, kidney failure). CKD staging also incorporates albuminuria categories (A1-A3) for more precise risk stratification. The combination of GFR stage and albuminuria category determines the risk of CKD progression, cardiovascular events, and the frequency of monitoring required.
Clinical applications of eGFR extend far beyond CKD diagnosis. It is essential for drug dosing adjustment, as many medications are cleared by the kidneys and require dose reduction in impaired renal function. eGFR guides decisions about contrast media administration, kidney biopsy, transplant evaluation, and initiation of renal replacement therapy. It is also a critical screening tool in patients with diabetes, hypertension, cardiovascular disease, and other conditions associated with kidney disease.
Important limitations of creatinine-based eGFR include its dependence on muscle mass (which varies with age, sex, nutrition, and chronic illness), its insensitivity to early kidney injury (creatinine does not rise until approximately 50% of function is lost), and interference from factors that alter creatinine generation or tubular secretion. Cystatin C-based equations may provide more accurate eGFR in patients with extremes of muscle mass, amputations, or other conditions that confound creatinine interpretation. The CKD-EPI 2021 equation using both creatinine and cystatin C provides the most accurate estimation when both markers are available.
The calculator implements the CKD-EPI 2021 creatinine equation: eGFR = 142 x min(Scr/kappa, 1)^alpha x max(Scr/kappa, 1)^(-1.200) x 0.9938^age x (1.012 if female). Kappa equals 0.7 for females and 0.9 for males. Alpha equals -0.241 for females and -0.302 for males. The equation uses the minimum of Scr/kappa or 1 raised to alpha and the maximum raised to -1.200 to create a two-slope relationship between creatinine and GFR.
eGFR is reported in mL/min/1.73 m2. Values above 90 are generally normal (Stage G1), though kidney damage can exist with normal GFR if albuminuria is present. eGFR 60-89 indicates mildly decreased function (G2). Below 60 is considered CKD if sustained for 3 or more months. eGFR below 15 indicates kidney failure. CKD staging should be combined with albuminuria assessment for complete risk classification.
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eGFR of 92.5 mL/min/1.73m2 is normal (Stage G1). Kidney function is well-preserved. Routine monitoring is appropriate unless albuminuria or other risk factors are present.
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eGFR of 28.3 indicates Stage G4 CKD with severely decreased kidney function. Nephrology referral, drug dose adjustments, and preparation for possible renal replacement therapy are indicated.
The 2021 CKD-EPI equation removed the race coefficient that was present in the 2009 version. The race variable had multiplied eGFR by 1.159 for Black patients. The 2021 equation was refit without race using diverse datasets, providing a single equation applicable to all racial and ethnic groups. This change was recommended by the NKF-ASN task force.
The CKD-EPI 2021 equation has a P30 (percentage of estimates within 30% of measured GFR) of approximately 89% overall. Accuracy is lower at higher GFR values (above 90) and in populations with atypical creatinine generation, such as those with muscle wasting, high muscle mass, or amputations.
Cystatin C-based eGFR should be considered when creatinine may be unreliable: extremes of muscle mass (bodybuilders, amputees, malnourished patients), high protein diets, patients taking drugs that inhibit creatinine secretion (trimethoprim, cimetidine), and when confirming CKD in patients with borderline creatinine-based eGFR near the diagnostic threshold of 60.
CKD is staged by GFR: G1 (above 90, normal), G2 (60-89, mildly decreased), G3a (45-59, mild-moderate), G3b (30-44, moderate-severe), G4 (15-29, severe), G5 (below 15, kidney failure). CKD diagnosis requires sustained abnormality for at least 3 months. Staging is combined with albuminuria categories A1-A3 for risk stratification.
The MDRD equation systematically underestimates GFR at values above 60, leading many laboratories to report these as simply >60 rather than an exact value. CKD-EPI is more accurate across the full GFR range, particularly in the 60-120 mL/min range where MDRD has the greatest bias, and is now the recommended equation by KDIGO guidelines.
eGFR is reported per 1.73 m2 body surface area (BSA), which is the standardized BSA for reporting. For drug dosing in patients with very different BSA (e.g., obese or very small patients), some guidelines recommend de-indexing by multiplying eGFR by the patient's BSA/1.73 to get absolute GFR in mL/min.
GFR naturally declines with aging at approximately 0.5-1.0 mL/min/1.73m2 per year after age 30-40. The 0.9938^age term in the CKD-EPI equation accounts for this decline. However, whether age-related GFR decline represents disease or normal aging remains debated, particularly when deciding whether to diagnose CKD in elderly patients with mild GFR reduction.
Yes, eGFR (CKD-EPI) is increasingly used for drug dosing, though some older drug labels reference creatinine clearance from the Cockcroft-Gault equation. For most drugs, CKD-EPI eGFR and Cockcroft-Gault CrCl yield similar dosing recommendations. When specific pharmacokinetic data references Cockcroft-Gault, that equation should be used.
GFR measures glomerular filtration alone, while creatinine clearance includes both filtration and tubular secretion of creatinine, making CrCl approximately 10-15% higher than true GFR. This difference is clinically significant mainly at low GFR levels. eGFR equations estimate true GFR, while Cockcroft-Gault estimates creatinine clearance.
Many laboratories report eGFR values above 120 as simply >120 because the equation has reduced accuracy at very high GFR. Hyperfiltration (eGFR above 120) can be a concern in early diabetic nephropathy, where elevated GFR paradoxically precedes GFR decline. However, in otherwise healthy young adults, values up to 140 are normal.
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