How is Gfr Calculated

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CKD-EPI GFR Calculator (2021 Equation)

mg/dL μmol/L
Male Female
Estimated GFR (eGFR):
mL/min/1.73 m²
function calculateGFR() { var scr = parseFloat(document.getElementById('scr_value').value); var unit = document.getElementById('scr_unit').value; var age = parseFloat(document.getElementById('patient_age').value); var sex = document.getElementById('patient_sex').value; var resultBox = document.getElementById('gfr_result_box'); var valueDisplay = document.getElementById('gfr_value'); var stageDisplay = document.getElementById('gfr_stage'); if (isNaN(scr) || isNaN(age) || scr <= 0 || age = 90) { stageText = "Stage G1: Normal or high function"; bgColor = "#27ae60"; } else if (finalResult >= 60) { stageText = "Stage G2: Mildly decreased"; bgColor = "#82c91e"; } else if (finalResult >= 45) { stageText = "Stage G3a: Mildly to moderately decreased"; bgColor = "#fab005"; textColor = "#000"; } else if (finalResult >= 30) { stageText = "Stage G3b: Moderately to severely decreased"; bgColor = "#f39c12"; } else if (finalResult >= 15) { stageText = "Stage G4: Severely decreased"; bgColor = "#e67e22"; } else { stageText = "Stage G5: Kidney failure"; bgColor = "#c0392b"; } stageDisplay.innerHTML = stageText; stageDisplay.style.backgroundColor = bgColor; stageDisplay.style.color = textColor; resultBox.style.backgroundColor = bgColor + "15"; // Very light version of the color }

Understanding How GFR is Calculated

Glomerular Filtration Rate (GFR) is widely considered the best overall index of kidney function. It measures how many milliliters of blood your kidneys filter per minute. Since direct measurement of GFR is complex and expensive, clinicians use "estimated GFR" (eGFR) calculated from serum biomarkers like creatinine.

The CKD-EPI 2021 Equation

The modern standard for calculating eGFR is the CKD-EPI 2021 Creatinine Equation. This specific formula was developed by the Chronic Kidney Disease Epidemiology Collaboration and is recommended by the National Kidney Foundation (NKF) because it provides an accurate assessment without the need for a race-based coefficient.

The formula uses three primary variables:

  • Serum Creatinine: A waste product from muscle breakdown that kidneys normally filter out.
  • Age: Kidney function naturally declines as we age.
  • Biological Sex: Adjusts for differences in muscle mass typically found between males and females.

Interpreting the Results: Kidney Function Stages

Kidney health is categorized into stages based on the eGFR value. A result of 60 or higher is generally considered in the normal range, while a result below 60 for three months or more may indicate chronic kidney disease (CKD).

Stage eGFR Range Description
G1 90+ Normal function
G2 60-89 Mild decrease
G3a 45-59 Mild-Moderate decrease
G3b 30-44 Moderate-Severe decrease
G4 15-29 Severe decrease
G5 < 15 Kidney failure

Why Does Accuracy Matter?

Calculating GFR accurately is vital for:

  • Diagnosing Chronic Kidney Disease (CKD) in early, treatable stages.
  • Adjusting medication dosages to prevent toxicity.
  • Monitoring the progression of existing kidney conditions.
  • Preparing for medical procedures involving contrast dyes.

Medical Disclaimer: This calculator is for educational purposes only. It should not be used for medical diagnosis or treatment decisions. Always consult with a healthcare professional regarding your kidney health and lab results.

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