GFR Kidney Function Calculator (CKD-EPI 2021)
Estimate your Glomerular Filtration Rate (GFR) using the CKD-EPI 2021 equation, which is a widely accepted method for assessing kidney function. This calculator requires your serum creatinine level, age, and sex.
Understanding GFR and Kidney Health
The Glomerular Filtration Rate (GFR) is a key indicator of kidney function. It measures how well your kidneys are filtering waste products from your blood. A higher GFR generally means healthier kidney function, while a lower GFR can indicate kidney disease.
What is GFR?
GFR represents the volume of fluid filtered from the blood into the Bowman's capsule per unit of time. It's expressed in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73 m²). This standardization helps compare kidney function across individuals of different sizes.
Why is GFR Important?
- Early Detection: GFR helps detect kidney disease early, often before symptoms appear.
- Monitoring Progression: It allows healthcare providers to monitor the progression of kidney disease over time.
- Treatment Planning: GFR values guide treatment decisions, including medication dosages and the timing of dialysis or transplant.
How is GFR Estimated?
Direct measurement of GFR is complex and rarely done in routine clinical practice. Instead, GFR is estimated using formulas that incorporate blood creatinine levels, age, sex, and sometimes race (though newer equations like CKD-EPI 2021 aim to be race-neutral). Creatinine is a waste product from muscle metabolism that healthy kidneys filter out of the blood. When kidney function declines, creatinine levels in the blood rise.
GFR Stages of Chronic Kidney Disease (CKD)
The National Kidney Foundation (NKF) classifies CKD into stages based on GFR:
- Stage 1: GFR ≥ 90 mL/min/1.73 m² – Normal kidney function, but with other signs of kidney damage (e.g., protein in urine).
- Stage 2: GFR 60-89 mL/min/1.73 m² – Mildly decreased kidney function, with other signs of kidney damage.
- Stage 3a: GFR 45-59 mL/min/1.73 m² – Mild-to-moderately decreased kidney function.
- Stage 3b: GFR 30-44 mL/min/1.73 m² – Moderately-to-severely decreased kidney function.
- Stage 4: GFR 15-29 mL/min/1.73 m² – Severely decreased kidney function.
- Stage 5: GFR < 15 mL/min/1.73 m² – Kidney failure (requiring dialysis or kidney transplant).
Example Calculations:
- Example 1: A 45-year-old female with a serum creatinine of 0.9 mg/dL.
GFR calculation would yield approximately 95 mL/min/1.73 m², indicating Stage 1 CKD (normal function with potential other signs).
- Example 2: A 60-year-old male with a serum creatinine of 1.5 mg/dL.
GFR calculation would yield approximately 50 mL/min/1.73 m², indicating Stage 3a CKD.
Disclaimer: This calculator provides an estimated GFR based on the CKD-EPI 2021 equation and is for informational purposes only. It 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.
.gfr-calculator-container {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 700px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e0e0e0;
border-radius: 10px;
background-color: #ffffff;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}
.gfr-calculator-container h2 {
color: #2c3e50;
text-align: center;
margin-bottom: 25px;
font-size: 1.8em;
}
.gfr-calculator-container h3 {
color: #34495e;
margin-top: 30px;
margin-bottom: 15px;
font-size: 1.4em;
}
.gfr-calculator-container h4 {
color: #34495e;
margin-top: 20px;
margin-bottom: 10px;
font-size: 1.2em;
}
.gfr-calculator-container p {
color: #555;
line-height: 1.6;
margin-bottom: 15px;
}
.calculator-form .form-group {
margin-bottom: 20px;
}
.calculator-form label {
display: block;
margin-bottom: 8px;
color: #333;
font-weight: bold;
}
.calculator-form input[type="number"] {
width: calc(100% – 22px);
padding: 12px;
border: 1px solid #ccc;
border-radius: 5px;
font-size: 1em;
box-sizing: border-box;
}
.calculator-form .radio-group {
display: flex;
gap: 20px;
align-items: center;
}
.calculator-form .radio-group input[type="radio"] {
margin-right: 5px;
transform: scale(1.2);
}
.calculator-form .radio-group label {
font-weight: normal;
margin-bottom: 0;
color: #555;
}
.calculator-form button {
width: 100%;
padding: 14px;
background-color: #28a745;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
.calculator-form button:hover {
background-color: #218838;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
border: 1px solid #d4edda;
background-color: #e9f7ef;
border-radius: 5px;
font-size: 1.1em;
color: #155724;
text-align: center;
font-weight: bold;
}
.calculator-result.error {
border-color: #f5c6cb;
background-color: #f8d7da;
color: #721c24;
}
.gfr-article-content ul {
list-style-type: disc;
margin-left: 20px;
color: #555;
}
.gfr-article-content ul li {
margin-bottom: 8px;
}
.gfr-article-content strong {
color: #333;
}
function calculateGFR() {
var serumCreatinineInput = document.getElementById("serumCreatinine");
var ageInput = document.getElementById("age");
var sexMale = document.getElementById("sexMale");
var sexFemale = document.getElementById("sexFemale");
var resultDiv = document.getElementById("gfrResult");
var serumCreatinine = parseFloat(serumCreatinineInput.value);
var age = parseInt(ageInput.value);
var sex = sexMale.checked ? "male" : "female";
// Input validation
if (isNaN(serumCreatinine) || serumCreatinine <= 0) {
resultDiv.innerHTML = "Please enter a valid Serum Creatinine value (e.g., 0.9 mg/dL).";
resultDiv.className = "calculator-result error";
return;
}
if (isNaN(age) || age 120) {
resultDiv.innerHTML = "Please enter a valid Age between 18 and 120 years.";
resultDiv.className = "calculator-result error";
return;
}
var kappa, alpha;
var femaleFactor = 1;
if (sex === "female") {
kappa = 0.7;
alpha = -0.241;
femaleFactor = 1.012;
} else { // male
kappa = 0.9;
alpha = -0.302;
femaleFactor = 1; // No factor for males
}
// CKD-EPI 2021 Equation
// GFR = 142 * min(Scr/κ, 1)^α * max(Scr/κ, 1)^-1.200 * 0.9938^Age * (1.012 if female)
var scrOverKappa = serumCreatinine / kappa;
var term1 = Math.pow(Math.min(scrOverKappa, 1), alpha);
var term2 = Math.pow(Math.max(scrOverKappa, 1), -1.200);
var term3 = Math.pow(0.9938, age);
var gfr = 142 * term1 * term2 * term3 * femaleFactor;
gfr = Math.round(gfr * 100) / 100; // Round to two decimal places
var gfrInterpretation = "";
var resultClass = "calculator-result";
if (gfr >= 90) {
gfrInterpretation = "
Stage 1: Normal kidney function (GFR ≥ 90 mL/min/1.73 m²).";
resultClass += " normal-gfr";
} else if (gfr >= 60) {
gfrInterpretation = "
Stage 2: Mildly decreased kidney function (GFR 60-89 mL/min/1.73 m²).";
resultClass += " mild-gfr";
} else if (gfr >= 45) {
gfrInterpretation = "
Stage 3a: Mild-to-moderately decreased kidney function (GFR 45-59 mL/min/1.73 m²).";
resultClass += " moderate-gfr";
} else if (gfr >= 30) {
gfrInterpretation = "
Stage 3b: Moderately-to-severely decreased kidney function (GFR 30-44 mL/min/1.73 m²).";
resultClass += " severe-gfr";
} else if (gfr >= 15) {
gfrInterpretation = "
Stage 4: Severely decreased kidney function (GFR 15-29 mL/min/1.73 m²).";
resultClass += " very-severe-gfr";
} else {
gfrInterpretation = "
Stage 5: Kidney failure (GFR < 15 mL/min/1.73 m²).";
resultClass += " failure-gfr";
}
resultDiv.innerHTML = "
Estimated GFR: " + gfr + " mL/min/1.73 m²
" + gfrInterpretation + "
This calculation uses the CKD-EPI 2021 equation.";
resultDiv.className = resultClass;
}