White
Black or African American
Other/Not Specified
Estimated GFR: — mL/min/1.73 m²
Understanding Glomerular Filtration Rate (GFR) and the MDRD Formula
The Glomerular Filtration Rate (GFR) is a crucial indicator of kidney function. It measures how much blood passes through the glomeruli – tiny filters in your kidneys – each minute. A normal GFR generally indicates healthy kidneys, while a low GFR can signal kidney disease or damage.
The MDRD (Modification of Diet in Renal Disease) Study equation is a widely used formula to estimate GFR. It's a more accurate method than older formulas and helps clinicians assess the stage of chronic kidney disease (CKD). The formula takes into account several key factors:
Serum Creatinine: A waste product from muscle metabolism, excreted by the kidneys. Higher levels often suggest reduced kidney function.
Age: GFR naturally tends to decline with age.
Gender: Differences in body composition can affect creatinine levels.
Race: Historically, race has been included in the MDRD formula due to observed differences in average muscle mass, though its use is increasingly debated and may be phased out in some updated guidelines.
The MDRD formula, in its original form for non-African Americans, is approximately:
GFR = 175 × (serum creatinine)^(-1.154) × (age)^(-0.203) × (0.742 if female) × (1.212 if black)
The result is typically reported in milliliters per minute per 1.73 square meters (mL/min/1.73 m²), which normalizes the filtration rate to a standard body surface area.
Interpreting GFR Values:
Stage 1: GFR 90 or above with kidney damage (e.g., protein in urine).
Stage 2: GFR 60-89 with kidney damage.
Stage 3a: GFR 45-59.
Stage 3b: GFR 30-44.
Stage 4: GFR 15-29 (Severe decrease in kidney function).
Stage 5: GFR less than 15 (Kidney failure).
Disclaimer: This calculator is for informational purposes only and does not substitute professional medical advice. Always consult with a qualified healthcare provider for diagnosis and treatment.
function calculateGFR() {
var serumCreatinine = parseFloat(document.getElementById("serumCreatinine").value);
var age = parseFloat(document.getElementById("age").value);
var gender = document.getElementById("gender").value;
var race = document.getElementById("race").value;
var gfrValue = "–";
if (isNaN(serumCreatinine) || isNaN(age) || serumCreatinine <= 0 || age <= 0) {
document.getElementById("gfrValue").textContent = "Invalid input. Please enter positive numbers for Serum Creatinine and Age.";
return;
}
var raceFactor = 1;
if (race === "black") {
raceFactor = 1.212;
}
var genderFactor = 1;
if (gender === "female") {
genderFactor = 0.742;
}
// Original MDRD equation constants
var k = -1.154; // for creatinine
var j = -0.203; // for age
var constant = 175;
// Calculate GFR using the MDRD formula
var gfr = constant * Math.pow(serumCreatinine, k) * Math.pow(age, j) * genderFactor * raceFactor;
gfrValue = gfr.toFixed(2); // Display with 2 decimal places
document.getElementById("gfrValue").textContent = gfrValue;
}
.gfr-calculator {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}
.gfr-calculator h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.input-group input[type="number"],
.input-group select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
.input-group select {
appearance: none;
background-color: white;
background-image: url('data:image/svg+xml;charset=US-ASCII,');
background-repeat: no-repeat;
background-position: right 10px top 50%;
}
.gfr-calculator button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
}
.gfr-calculator button:hover {
background-color: #0056b3;
}
.calculator-results {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
}
.calculator-results h3 {
margin: 0;
color: #333;
}
#gfrValue {
font-size: 1.5rem;
font-weight: bold;
color: #28a745;
}
.calculator-explanation {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
color: #666;
font-size: 0.95rem;
line-height: 1.6;
}
.calculator-explanation h3, .calculator-explanation h4 {
color: #333;
margin-bottom: 10px;
}
.calculator-explanation ul {
margin-left: 20px;
padding-left: 0;
}
.calculator-explanation li {
margin-bottom: 8px;
}