How to Calculate Glomerular Filtration Rate Gfr

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GFR Calculator (CKD-EPI 2021)

Estimate kidney function based on the latest clinical standards.

Male Female
Estimated GFR: mL/min/1.73m²

What is Glomerular Filtration Rate (GFR)?

Glomerular Filtration Rate (GFR) is the best overall index of kidney function. It measures how many milliliters of blood the kidneys filter per minute. A normal GFR for an adult is typically above 90 mL/min/1.73m², although this naturally declines with age.

How to Calculate GFR

This calculator uses the CKD-EPI (2021) Creatinine Equation. This is the current recommended standard by the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) because it does not include a race variable, making it more equitable and accurate for a diverse population.

The mathematical formula is complex, involving the following components:

  • Serum Creatinine: A waste product from muscle breakdown filtered by the kidneys.
  • Age: Kidney function naturally decreases as we get older.
  • Sex: Males generally have higher muscle mass and creatinine production than females.

Understanding the Results (CKD Stages)

Doctors use GFR to categorize Chronic Kidney Disease (CKD) into five stages:

Stage GFR Range Description
Stage 1 90+ Normal or high function (with evidence of kidney damage)
Stage 2 60-89 Mildly decreased function
Stage 3a 45-59 Mildly to moderately decreased function
Stage 3b 30-44 Moderately to severely decreased function
Stage 4 15-29 Severely decreased function
Stage 5 Below 15 Kidney failure (End-stage renal disease)

Example Calculation

If a 55-year-old female has a serum creatinine of 1.2 mg/dL:

  1. The formula adjusts for the specific constants for females (κ = 0.7).
  2. The calculation yields an estimated GFR of approximately 56 mL/min/1.73m².
  3. This would place the patient in Stage 3a (Mildly to Moderately decreased).

Note: This tool is for informational purposes and should not replace professional medical advice. Always consult with a healthcare provider regarding kidney health.

function calculateKidneyFunction() { var scr = parseFloat(document.getElementById('serum_creatinine').value); var age = parseFloat(document.getElementById('gfr_age').value); var gender = document.getElementById('gfr_gender').value; var resultBox = document.getElementById('gfr-result-box'); var gfrDisplay = document.getElementById('gfr_value'); var stageDisplay = document.getElementById('gfr_stage'); if (isNaN(scr) || isNaN(age) || scr <= 0 || age = 90) { stageText = "Stage 1: Normal Function"; stageColor = "#28a745"; } else if (finalGfr >= 60) { stageText = "Stage 2: Mild Decrease"; stageColor = "#9dc33b"; } else if (finalGfr >= 45) { stageText = "Stage 3a: Mild-Moderate Decrease"; stageColor = "#ffc107"; } else if (finalGfr >= 30) { stageText = "Stage 3b: Moderate-Severe Decrease"; stageColor = "#fd7e14"; } else if (finalGfr >= 15) { stageText = "Stage 4: Severe Decrease"; stageColor = "#dc3545"; } else { stageText = "Stage 5: Kidney Failure"; stageColor = "#721c24"; } stageDisplay.innerText = stageText; stageDisplay.style.backgroundColor = stageColor; resultBox.style.display = "block"; resultBox.style.border = "2px solid " + stageColor; resultBox.style.backgroundColor = stageColor + "10"; // Light transparency }

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