Estimate your Glomerular Filtration Rate (GFR) using the CKD-EPI 2009 formula. GFR is a key indicator of kidney function.
Understanding GFR and Kidney Health
The Glomerular Filtration Rate (GFR) is a crucial measure of how well your kidneys are filtering waste products from your blood. It indicates the volume of fluid filtered from the blood into the Bowman's capsule per unit of time. A healthy GFR is essential for maintaining overall health, as kidneys play a vital role in removing toxins, balancing electrolytes, and regulating blood pressure.
Why is GFR Important?
Monitoring GFR helps healthcare professionals:
Detect Kidney Disease Early: A declining GFR can be an early sign of chronic kidney disease (CKD), often before symptoms appear.
Stage Kidney Disease: GFR values are used to classify the stages of CKD, which guides treatment and management plans.
Monitor Disease Progression: Regular GFR measurements help track how quickly kidney disease is progressing.
Adjust Medication Dosages: Many medications are cleared by the kidneys, and dosages may need adjustment based on GFR to prevent accumulation and toxicity.
How is GFR Calculated? (CKD-EPI 2009 Formula)
Directly measuring GFR is complex and usually involves injecting a marker substance. Therefore, GFR is typically estimated using formulas that incorporate readily available blood test results and patient characteristics. The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2009 equation is one of the most widely accepted and accurate formulas for estimating GFR.
This calculator uses the CKD-EPI 2009 formula, which considers:
Serum Creatinine (mg/dL): Creatinine is a waste product from muscle metabolism. Healthy kidneys filter creatinine efficiently, so higher levels in the blood can indicate reduced kidney function.
Age (years): Kidney function naturally declines with age.
Sex: Biological sex influences muscle mass and, consequently, creatinine levels.
Race (African American vs. Non-African American): The original CKD-EPI 2009 formula included a race coefficient, as studies showed differences in creatinine levels between racial groups. However, it's important to note that the use of race in GFR equations is a subject of ongoing debate and newer formulas are being developed to remove race-based adjustments. This calculator uses the original 2009 formula which includes this factor.
Interpreting Your GFR Results
GFR is measured in milliliters per minute per 1.73 square meters (mL/min/1.73 m²), which adjusts for average body surface area. Here's a general guide to interpreting GFR values:
GFR ≥ 90: Normal kidney function.
GFR 60-89: Mildly decreased kidney function. Often, no symptoms are present, but it's important to monitor.
GFR 45-59: Mild to moderate decrease in kidney function (CKD Stage 3a).
GFR 30-44: Moderate to severe decrease in kidney function (CKD Stage 3b).
GFR 15-29: Severely decreased kidney function (CKD Stage 4).
GFR < 15: Kidney failure (CKD Stage 5), often requiring dialysis or kidney transplant.
Important Disclaimer: This calculator provides an estimate of GFR based on the CKD-EPI 2009 formula. It is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider for any health concerns or before making any decisions related to your health or treatment.
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function calculateGFR() {
var serumCreatinineInput = document.getElementById("serumCreatinine");
var ageInput = document.getElementById("age");
var gfrResultDiv = document.getElementById("gfrResult");
var scr = parseFloat(serumCreatinineInput.value);
var age = parseInt(ageInput.value);
var sexFemale = document.getElementById("sexFemale").checked;
var sexMale = document.getElementById("sexMale").checked;
var raceAA = document.getElementById("raceAA").checked;
var raceNonAA = document.getElementById("raceNonAA").checked;
// Input validation
if (isNaN(scr) || scr <= 0) {
gfrResultDiv.innerHTML = "Please enter a valid Serum Creatinine (e.g., 0.1 or higher).";
gfrResultDiv.className = "calculator-result error";
return;
}
if (isNaN(age) || age 120) {
gfrResultDiv.innerHTML = "Please enter a valid Age (18-120 years).";
gfrResultDiv.className = "calculator-result error";
return;
}
if (!sexFemale && !sexMale) {
gfrResultDiv.innerHTML = "Please select your Sex.";
gfrResultDiv.className = "calculator-result error";
return;
}
if (!raceAA && !raceNonAA) {
gfrResultDiv.innerHTML = "Please select your Race.";
gfrResultDiv.className = "calculator-result error";
return;
}
var GFR;
var kappa; // Kappa is 0.7 for females, 0.9 for males
var alpha; // Alpha is -0.329 for females, -0.411 for males
var constant; // Constant is 144 for females, 141 for males
if (sexFemale) {
kappa = 0.7;
alpha = -0.329;
constant = 144;
} else { // Male
kappa = 0.9;
alpha = -0.411;
constant = 141;
}
var minScrPower;
var maxScrPower;
if (scr / kappa <= 1) {
minScrPower = Math.pow(scr / kappa, alpha);
maxScrPower = Math.pow(1, -1.209); // (1)^-1.209 is 1
} else {
minScrPower = Math.pow(1, alpha); // (1)^alpha is 1
maxScrPower = Math.pow(scr / kappa, -1.209);
}
// CKD-EPI 2009 formula
// GFR = 141 * min(Scr/κ, 1)^α * max(Scr/κ, 1)^-1.209 * 0.993^Age * [1.018 if female] * [1.159 if Black]
// Note: The formula is slightly different for males/females and the powers.
// Let's re-implement based on standard CKD-EPI 2009:
var GFR_base;
if (sexFemale) {
if (scr <= 0.7) {
GFR_base = 144 * Math.pow(scr / 0.7, -0.329) * Math.pow(0.993, age);
} else {
GFR_base = 144 * Math.pow(scr / 0.7, -1.209) * Math.pow(0.993, age);
}
} else { // Male
if (scr <= 0.9) {
GFR_base = 141 * Math.pow(scr / 0.9, -0.411) * Math.pow(0.993, age);
} else {
GFR_base = 141 * Math.pow(scr / 0.9, -1.209) * Math.pow(0.993, age);
}
}
// Apply race factor
if (raceAA) {
GFR = GFR_base * 1.159;
} else {
GFR = GFR_base;
}
gfrResultDiv.innerHTML = "Estimated GFR: " + GFR.toFixed(2) + " mL/min/1.73 m²";
gfrResultDiv.className = "calculator-result";
}