Kidney function is a vital indicator of overall health. The most effective way to measure how well your kidneys are filtering blood is by calculating the Glomerular Filtration Rate (eGFR). This calculator uses the CKD-EPI 2021 (Race-Free) equation, which is currently recommended by the National Kidney Foundation for providing the most accurate estimate of kidney function in adults.
What is Serum Creatinine?
Creatinine is a waste product generated by your muscles from the breakdown of a compound called creatine. Your kidneys are responsible for filtering creatinine out of your blood and excreting it through urine. Because muscle mass remains relatively constant, creatinine levels in the blood tend to be stable unless kidney function changes.
Low Creatinine: May indicate low muscle mass or malnutrition.
High Creatinine: Often indicates impaired kidney function or dehydration.
Normal Ranges for Creatinine
Normal serum creatinine levels vary depending on age, gender, and muscle mass. General reference ranges are typically:
Group
Range (mg/dL)
Range (µmol/L)
Adult Men
0.74 to 1.35 mg/dL
65.4 to 119.3 µmol/L
Adult Women
0.59 to 1.04 mg/dL
52.2 to 91.9 µmol/L
What is eGFR?
The estimated Glomerular Filtration Rate (eGFR) mathematically converts your serum creatinine level, age, and gender into a single number representing kidney filtration efficiency. It is measured in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²).
Kidney Disease Stages based on eGFR
The eGFR value helps classify Chronic Kidney Disease (CKD) into five stages:
Stage 1 (eGFR > 90): Normal or high kidney function. If protein is present in urine, it may still indicate kidney damage.
Stage 2 (eGFR 60-89): Mild decrease in kidney function.
Stage 3a (eGFR 45-59): Mild to moderate decrease in kidney function.
Stage 3b (eGFR 30-44): Moderate to severe decrease in kidney function.
Stage 4 (eGFR 15-29): Severe decrease in kidney function. Preparation for dialysis or transplant is usually discussed.
Stage 5 (eGFR < 15): Kidney failure (End Stage Renal Disease). Dialysis or transplant is necessary for survival.
When to Consult a Doctor
This calculator is a screening tool and not a diagnosis. Factors such as extreme diet (high protein), unusual muscle mass (bodybuilders or amputees), or specific medications can affect creatinine levels. If your eGFR is below 60 for more than three months, or if you have concerns about your kidney health, consult a nephrologist or healthcare provider immediately.
function calculateEGFR() {
// Get Input Values
var gender = document.getElementById('egfrGender').value;
var age = parseFloat(document.getElementById('egfrAge').value);
var creatinineInput = parseFloat(document.getElementById('egfrCreatinine').value);
var unit = document.getElementById('egfrUnit').value;
// Validation
if (isNaN(age) || isNaN(creatinineInput) || age <= 0 || creatinineInput <= 0) {
alert("Please enter valid positive numbers for Age and Creatinine.");
return;
}
// Convert Creatinine to mg/dL if necessary
// 1 mg/dL = 88.4 µmol/L
var scr = creatinineInput;
if (unit === 'umol') {
scr = creatinineInput / 88.4;
}
// CKD-EPI 2021 Constants
var kappa, alpha, genderFactor;
if (gender === 'female') {
kappa = 0.7;
alpha = -0.241;
genderFactor = 1.012;
} else {
kappa = 0.9;
alpha = -0.302;
genderFactor = 1;
}
// The Formula:
// eGFR = 142 * min(Scr/k, 1)^a * max(Scr/k, 1)^-1.200 * 0.9938^Age * genderFactor
var ratio = scr / kappa;
var term1 = Math.pow(Math.min(ratio, 1), alpha);
var term2 = Math.pow(Math.max(ratio, 1), -1.200);
var term3 = Math.pow(0.9938, age);
var eGFR = 142 * term1 * term2 * term3 * genderFactor;
// Rounding
eGFR = Math.round(eGFR);
// Determine Stage and Display Logic
var resultDiv = document.getElementById('egfrResult');
var numericDiv = document.getElementById('numericResult');
var stageDiv = document.getElementById('stageResult');
var interpDiv = document.getElementById('interpretationText');
resultDiv.style.display = 'block';
numericDiv.innerHTML = eGFR + ' mL/min/1.73m²';
var stageText = "";
var badgeClass = "";
var explanation = "";
if (eGFR >= 90) {
stageText = "Stage 1: Normal Function";
badgeClass = "stage-green";
explanation = "Your calculated eGFR indicates normal or high kidney function. Note: Kidney disease may still be present if you have other signs like protein in the urine.";
} else if (eGFR >= 60) {
stageText = "Stage 2: Mild Decrease";
badgeClass = "stage-green";
explanation = "Mild decrease in kidney function. This can be age-related but should be monitored.";
} else if (eGFR >= 45) {
stageText = "Stage 3a: Mild to Moderate";
badgeClass = "stage-yellow";
explanation = "Mild to moderate loss of kidney function.";
} else if (eGFR >= 30) {
stageText = "Stage 3b: Moderate to Severe";
badgeClass = "stage-orange";
explanation = "Moderate to severe loss of kidney function. Medical attention is required.";
} else if (eGFR >= 15) {
stageText = "Stage 4: Severe Decrease";
badgeClass = "stage-red";
explanation = "Severe reduction in kidney function. Preparation for renal replacement therapy typically begins here.";
} else {
stageText = "Stage 5: Kidney Failure";
badgeClass = "stage-red";
explanation = "Kidney failure (End Stage Renal Disease). Dialysis or transplant is likely needed.";
}
stageDiv.innerHTML = stageText + ' ' + eGFR + '';
interpDiv.innerText = explanation;
}