GFR Calculator

Calculate Glomerular Filtration Rate (GFR) to assess kidney function. Uses MDRD and CKD-EPI equations for accurate estimation of renal function and disease staging.

Measurement Guide

  1. Enter serum creatinine level
  2. Input age and gender
  3. Select ethnicity factors
  4. Review GFR result
  5. Check kidney function stage

Renal Physiology and GFR

Glomerular Filtration Rate (GFR) represents the fundamental measure of kidney function, quantifying the volume of plasma filtered by the glomeruli per unit time. This physiological parameter reflects the complex interaction between renal blood flow, filtration pressure, and glomerular membrane permeability. Understanding GFR provides crucial insights into kidney health and overall fluid-electrolyte homeostasis.

Normal GFR Values by Age:

  • • Young Adults: 120-130 mL/min/1.73m²
  • • Middle Age: 90-120 mL/min/1.73m²
  • • Elderly: Natural decline ~1 mL/min/year

Estimation Methods and Equations

Multiple equations have been developed to estimate GFR, each with specific advantages and limitations. These formulas incorporate various demographic and laboratory parameters to approximate true GFR:

MDRD Equation:

GFR = 175 × Scr^(-1.154) × age^(-0.203) × [0.742 if female] × [1.212 if black]

CKD-EPI Equation:

GFR = 141 × min(Scr/κ,1)^α × max(Scr/κ,1)^(-1.209) × 0.993^age × [1.018 if female] × [1.159 if black]

Cockcroft-Gault:

CrCl = [(140-age) × weight] / (72 × Scr) × [0.85 if female]

Clinical Interpretation

GFR interpretation requires understanding of both physiological and pathological contexts. Chronic Kidney Disease (CKD) staging is based on GFR values, providing a framework for clinical decision-making and therapeutic interventions:

CKD Staging by GFR:

  • • Stage 1: ≥90 mL/min (Normal with kidney damage)
  • • Stage 2: 60-89 mL/min (Mild reduction)
  • • Stage 3a: 45-59 mL/min (Mild-moderate reduction)
  • • Stage 3b: 30-44 mL/min (Moderate-severe reduction)
  • • Stage 4: 15-29 mL/min (Severe reduction)
  • • Stage 5: <15 mL/min (Kidney failure)

Factors Affecting GFR

Multiple physiological and pathological factors can influence GFR measurements and interpretation. Understanding these variables is crucial for accurate assessment of kidney function:

Modifying Factors:

  • • Age-related changes in kidney function
  • • Muscle mass effects on creatinine generation
  • • Dietary protein intake variations
  • • Medications affecting renal hemodynamics
  • • Acute illness and volume status

Advanced Considerations

Modern approaches to GFR assessment incorporate additional biomarkers and sophisticated modeling techniques. These advanced methods aim to improve accuracy and account for limitations of traditional estimation equations:

Emerging Approaches:

  • • Cystatin C-based equations
  • • Combined creatinine-cystatin C formulas
  • • Beta-trace protein measurements
  • • Artificial intelligence modeling

These developments reflect ongoing efforts to enhance the precision and clinical utility of GFR estimation in diverse patient populations.