function calculateGFR() {
var scrInput = document.getElementById('scr').value;
var unit = document.getElementById('unit').value;
var age = document.getElementById('age').value;
var gender = document.getElementById('gender').value;
var resultBox = document.getElementById('resultBox');
var gfrValueDisplay = document.getElementById('gfrValue');
var stageInfoDisplay = document.getElementById('stageInfo');
var interpretationDisplay = document.getElementById('interpretation');
// Validation
if (!scrInput || !age) {
alert("Please enter both Serum Creatinine and Age.");
return;
}
var scr = parseFloat(scrInput);
var ageNum = parseInt(age);
if (scr <= 0 || ageNum = 90) {
stageText = "Stage 1: Normal or high";
stageClass = "stage-1";
interpText = "Kidney function is normal, but other signs of kidney damage may be present.";
} else if (gfrRounded >= 60) {
stageText = "Stage 2: Mildly decreased";
stageClass = "stage-2";
interpText = "Kidney function is mildly reduced.";
} else if (gfrRounded >= 45) {
stageText = "Stage 3a: Mildly to moderately decreased";
stageClass = "stage-3a";
interpText = "Mild to moderate loss of kidney function.";
} else if (gfrRounded >= 30) {
stageText = "Stage 3b: Moderately to severely decreased";
stageClass = "stage-3b";
interpText = "Moderate to severe loss of kidney function.";
} else if (gfrRounded >= 15) {
stageText = "Stage 4: Severely decreased";
stageClass = "stage-4";
interpText = "Severe loss of kidney function. Preparation for renal replacement therapy is usually required.";
} else {
stageText = "Stage 5: Kidney failure";
stageClass = "stage-5";
interpText = "Kidney failure (End Stage Renal Disease). Dialysis or transplant usually required.";
}
// Update DOM
gfrValueDisplay.textContent = gfrRounded;
stageInfoDisplay.className = "stage-indicator " + stageClass;
stageInfoDisplay.textContent = stageText;
interpretationDisplay.textContent = interpText;
resultBox.style.display = "block";
}
How to Calculate Glomerular Filtration Rate (eGFR)
Understanding your kidney health is vital for long-term well-being. The Glomerular Filtration Rate (GFR) is the single best test to measure your level of kidney function and determine your stage of kidney disease. This guide explains how GFR is calculated, the variables involved, and what the results mean for your health.
What is GFR?
Glomerular Filtration Rate (GFR) represents the flow rate of filtered fluid through the kidney. Specifically, it measures how much blood your glomeruli (tiny filters inside the kidneys) clean every minute.
Since measuring the exact GFR directly requires complex and lengthy procedures (like injecting inulin), medical professionals use an Estimated GFR (eGFR) based on a blood test for creatinine.
The CKD-EPI 2021 Formula
In 2021, the National Kidney Foundation and the American Society of Nephrology recommended a new equation for estimating GFR that does not include a race coefficient. This calculator uses the CKD-EPI 2021 Creatinine Equation, which is currently the standard for evaluating kidney function.
Scr (Serum Creatinine): A waste product produced by muscles from the breakdown of a compound called creatine. Healthy kidneys filter creatinine out of the blood.
Age: Kidney function naturally declines slightly with age.
Gender: Muscle mass differences between males and females affect creatinine generation.
κ (Kappa): 0.7 for females, 0.9 for males.
α (Alpha): -0.241 for females, -0.302 for males.
Understanding Kidney Disease Stages
Your GFR result helps categorize kidney function into five stages of Chronic Kidney Disease (CKD). A lower number indicates less kidney function.
Stage
GFR Range
Description
Stage 1
90+
Normal or high function (if kidney damage is present)
Stage 2
60-89
Mildly decreased function
Stage 3a
45-59
Mild to moderate decrease
Stage 3b
30-44
Moderate to severe decrease
Stage 4
15-29
Severely decreased function
Stage 5
Below 15
Kidney failure (requires dialysis or transplant)
Why Use Creatinine?
Creatinine is the primary marker used because it is produced by your body at a relatively constant rate. If your kidneys are not functioning properly, creatinine builds up in the blood. Therefore, high serum creatinine levels usually correlate with a low GFR.
However, because muscle mass affects creatinine production, the calculation must adjust for age and gender. For example, a young male with high muscle mass will produce more creatinine than an older female with low muscle mass, even if their kidney function is identical.
Limitations of eGFR
While the eGFR calculator is an excellent screening tool, it has limitations:
Muscle Mass: Bodybuilders or amputees may have creatinine levels that do not accurately reflect kidney function.
Diet: High protein intake or creatine supplements can temporarily raise creatinine levels.
Acute Kidney Injury (AKI): eGFR is not accurate for patients with rapidly changing kidney function (e.g., hospitalized patients with AKI).
When to See a Doctor
An eGFR below 60 mL/min/1.73 m² for three months or more is a sign of chronic kidney disease. If your calculated GFR is low, consult a nephrologist. They may order additional tests, such as a urine albumin-to-creatinine ratio (uACR) or a Cystatin C test, to confirm the diagnosis and determine the cause.