function calculateEGFR() {
// Get Inputs
var scrInput = document.getElementById('scrInput').value;
var unit = document.getElementById('unitSelect').value;
var age = document.getElementById('ageInput').value;
var gender = document.getElementById('genderSelect').value;
var resultBox = document.getElementById('resultBox');
var gfrDisplay = document.getElementById('gfrResult');
var stageBadge = document.getElementById('stageBadge');
var stageDesc = document.getElementById('stageDescription');
// Validation
if (!scrInput || !age || scrInput <= 0 || age = 90) {
stageText = "Stage 1: Normal or High";
stageClass = "stage-1";
description = "Kidney function is normal, but other signs of kidney damage might be present.";
} else if (finalGFR >= 60) {
stageText = "Stage 2: Mildly Decreased";
stageClass = "stage-2";
description = "Mild loss of kidney function. Observation and monitoring recommended.";
} else if (finalGFR >= 45) {
stageText = "Stage 3a: Mild to Moderate";
stageClass = "stage-3a";
description = "Mild to moderate loss of kidney function. Treatment may be needed to slow progression.";
} else if (finalGFR >= 30) {
stageText = "Stage 3b: Moderate to Severe";
stageClass = "stage-3b";
description = "Moderate to severe loss of kidney function. Closer monitoring by a nephrologist is advised.";
} else if (finalGFR >= 15) {
stageText = "Stage 4: Severely Decreased";
stageClass = "stage-4";
description = "Severe loss of kidney function. Preparation for kidney failure treatment usually begins.";
} else {
stageText = "Stage 5: Kidney Failure";
stageClass = "stage-5";
description = "Kidney failure (End Stage Renal Disease). Dialysis or transplant is likely needed.";
}
// Update Badge
stageBadge.className = "stage-badge " + stageClass;
stageBadge.innerHTML = stageText;
stageDesc.innerHTML = description;
}
eGFR Calculation and Understanding Kidney Function
The Estimated Glomerular Filtration Rate (eGFR) is widely considered the best overall index of kidney function. It provides a numerical estimate of how well your kidneys are filtering wastes from your blood. This calculator uses the CKD-EPI 2021 Creatinine Equation, which is currently recommended by the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) as it removes race as a variable for a more equitable diagnosis.
How is eGFR Calculated?
The calculation is based on a complex formula that takes into account several key biological factors. Unlike simple ratios, the eGFR formula adjusts for variables that naturally affect muscle mass and creatinine generation.
Formula Used (CKD-EPI 2021):
eGFR = 142 × min(Scr/κ, 1)α × max(Scr/κ, 1)-1.200 × 0.9938Age × 1.012 [if female]
Input Variables Explained
Serum Creatinine (Scr): Creatinine is a waste product generated by muscle metabolism. Healthy kidneys filter it out of the blood. High levels in the blood suggest the kidneys are not filtering effectively.
Age: Kidney function naturally declines slightly with age. The formula adjusts for this expected physiological change.
Sex: On average, biological males have higher muscle mass than females, leading to higher baseline creatinine generation. The formula uses different coefficients (κ and α) to standardize the result.
Understanding Your eGFR Results
The result is measured in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²). This number generally corresponds to the percentage of available kidney function.
eGFR Range
CKD Stage
Description
90+
Stage 1
Normal or high kidney function.
60 – 89
Stage 2
Mildly decreased function.
45 – 59
Stage 3a
Mild to moderate decrease.
30 – 44
Stage 3b
Moderate to severe decrease.
15 – 29
Stage 4
Severely decreased function.
Below 15
Stage 5
Kidney failure (requires dialysis or transplant).
Clinical Note on Race and eGFR
Historically, eGFR equations (such as the MDRD or CKD-EPI 2009) included a multiplier for Black patients, based on the assumption that Black individuals had higher muscle mass and creatinine generation. However, in 2021, the National Kidney Foundation and the American Society of Nephrology recommended removing the race coefficient to prevent delayed diagnosis and ensure health equity. The calculator above utilizes this modern race-free 2021 equation.
When Should You See a Doctor?
An eGFR below 60 mL/min/1.73m² for three months or more is a diagnostic criterion for Chronic Kidney Disease (CKD). However, a single test result is not a diagnosis. Dehydration, diet, and medication can temporarily affect creatinine levels. If your calculated eGFR is abnormal:
Retest: Doctors usually repeat the test to confirm the result.
Check Urine Albumin: A urine test for protein (albumin) helps assess kidney damage.
Review Medications: Some drugs, such as NSAIDs (ibuprofen), can impact kidney function.
Disclaimer: This tool is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always interpret laboratory results in consultation with a qualified healthcare professional.