function calculateGFR() {
// 1. Get input values
var scr = parseFloat(document.getElementById("scrInput").value);
var age = parseFloat(document.getElementById("ageInput").value);
var gender = document.getElementById("genderInput").value;
var resultBox = document.getElementById("resultBox");
var gfrDisplay = document.getElementById("gfrValue");
var stageDisplay = document.getElementById("stageValue");
// 2. Validate inputs
if (isNaN(scr) || scr <= 0) {
alert("Please enter a valid positive number for Serum Creatinine.");
return;
}
if (isNaN(age) || age = 90) {
stage = "Stage 1: Normal or high kidney function";
color = "#d4edda"; // Light green
} else if (gfr >= 60) {
stage = "Stage 2: Mildly decreased kidney function";
color = "#fff3cd"; // Light yellow
} else if (gfr >= 45) {
stage = "Stage 3a: Mild to moderately decreased";
color = "#ffeeba"; // Yellow-orange
} else if (gfr >= 30) {
stage = "Stage 3b: Moderate to severely decreased";
color = "#f8d7da"; // Light red
} else if (gfr >= 15) {
stage = "Stage 4: Severely decreased kidney function";
color = "#f5c6cb"; // Red
} else {
stage = "Stage 5: Kidney failure";
color = "#ffb3b3"; // Darker red
}
// 6. Display Results
resultBox.style.display = "block";
gfrDisplay.innerHTML = gfr.toFixed(1);
stageDisplay.innerHTML = stage;
stageDisplay.style.backgroundColor = color;
}
Understanding the Glomerular Filtration Rate (GFR) Calculation
The Glomerular Filtration Rate (GFR) is widely considered the best overall index of kidney function. It measures how much blood passes through the glomeruli—the tiny filters in the kidneys that remove waste from the blood—each minute. Because GFR is difficult to measure directly, medical professionals utilize an estimated GFR (eGFR) derived from mathematical formulas based on blood test results.
The CKD-EPI 2021 Equation
This calculator utilizes the CKD-EPI 2021 Creatinine Equation, which is currently recommended by the National Kidney Foundation and the American Society of Nephrology. This modern formula replaces older equations like the MDRD or Cockcroft-Gault equations for general adult screening.
The calculation relies on the following variables:
Serum Creatinine (Scr): A waste product produced by muscles from the breakdown of a compound called creatine. Healthy kidneys filter creatinine out of the blood. Higher levels typically indicate lower kidney function.
Age: GFR naturally declines with age, and the formula accounts for this physiological change.
Biological Sex: Muscle mass differences between males and females affect creatinine production, which necessitates different coefficients in the formula.
Interpreting GFR Results
The result is expressed in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73 m²). This standardized unit allows for consistent comparison across different body sizes.
GFR > 90: Normal or high kidney function. If there are other signs of kidney damage (like protein in urine), this is Stage 1.
GFR 60-89: Mildly decreased kidney function (Stage 2).
GFR 45-59: Mild to moderate decrease (Stage 3a).
GFR 30-44: Moderate to severe decrease (Stage 3b).
GFR 15-29: Severely decreased kidney function (Stage 4).
GFR < 15: Kidney failure (Stage 5), often requiring dialysis or transplant.
Why is GFR Important?
Early detection of Chronic Kidney Disease (CKD) is crucial because symptoms often do not appear until the disease is advanced. Regular monitoring of GFR allows doctors to detect declining function early, manage risk factors (such as hypertension and diabetes), and potentially slow the progression of kidney damage.
Medical Disclaimer: This calculator is for educational and informational purposes only. It does not constitute medical advice, diagnosis, or treatment. The results generated by this tool should not be used as a substitute for professional medical consultation. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.