GFR Calculator (CKD-EPI 2021)
Use this calculator to estimate your Glomerular Filtration Rate (GFR) based on your serum creatinine, age, and sex, using the CKD-EPI 2021 equation recommended by the National Kidney Foundation. GFR is a key indicator of kidney function.
function calculateGFR() {
var creatinineInput = document.getElementById("creatinine").value;
var ageInput = document.getElementById("age").value;
var sex = document.getElementById("sex").value;
var creatinine = parseFloat(creatinineInput);
var age = parseInt(ageInput);
var gfrResultDiv = document.getElementById("gfrResult");
var gfrInterpretationDiv = document.getElementById("gfrInterpretation");
gfrResultDiv.innerHTML = "";
gfrInterpretationDiv.innerHTML = "";
if (isNaN(creatinine) || creatinine <= 0) {
gfrResultDiv.innerHTML = "
Please enter a valid positive Serum Creatinine value.";
return;
}
if (isNaN(age) || age 120) {
gfrResultDiv.innerHTML = "
Please enter a valid age between 18 and 120 years.";
return;
}
if (sex === "") {
gfrResultDiv.innerHTML = "
Please select your sex.";
return;
}
var kappa, alpha, sexFactor;
if (sex === "female") {
kappa = 0.7;
alpha = -0.241;
sexFactor = 1.012;
} else { // male
kappa = 0.9;
alpha = -0.302;
sexFactor = 1; // No additional factor for males
}
var min_scr_kappa = Math.min(creatinine / kappa, 1);
var max_scr_kappa = Math.max(creatinine / kappa, 1);
var gfr = 142 * Math.pow(min_scr_kappa, alpha) * Math.pow(max_scr_kappa, -1.200) * Math.pow(0.9938, age);
if (sex === "female") {
gfr = gfr * sexFactor;
}
gfrResultDiv.innerHTML = "
" + gfr.toFixed(2) + " mL/min/1.73m²";
interpretGFR(gfr, gfrInterpretationDiv);
}
function interpretGFR(gfrValue, interpretationDiv) {
var interpretationText = "";
if (gfrValue >= 90) {
interpretationText = "
Stage 1: Normal or High GFR (≥90 mL/min/1.73m²). This indicates normal kidney function. Continue healthy lifestyle practices.";
} else if (gfrValue >= 60 && gfrValue < 90) {
interpretationText = "
Stage 2: Mildly Decreased GFR (60-89 mL/min/1.73m²). This indicates mildly reduced kidney function. Monitor regularly and discuss with your doctor.";
} else if (gfrValue >= 45 && gfrValue < 60) {
interpretationText = "
Stage 3a: Mild-to-Moderately Decreased GFR (45-59 mL/min/1.73m²). This indicates mild to moderate kidney damage. Regular monitoring and management are important.";
} else if (gfrValue >= 30 && gfrValue < 45) {
interpretationText = "
Stage 3b: Moderately-to-Severely Decreased GFR (30-44 mL/min/1.73m²). This indicates moderate to severe kidney damage. Close medical supervision is recommended.";
} else if (gfrValue >= 15 && gfrValue < 30) {
interpretationText = "
Stage 4: Severely Decreased GFR (15-29 mL/min/1.73m²). This indicates severe kidney damage. Prepare for kidney failure and discuss treatment options with your doctor.";
} else if (gfrValue < 15) {
interpretationText = "
Stage 5: Kidney Failure (<15 mL/min/1.73m²). This indicates kidney failure, requiring dialysis or kidney transplant. Urgent medical attention is needed.";
} else {
interpretationText = "Unable to interpret GFR. Please ensure valid inputs.";
}
interpretationDiv.innerHTML = interpretationText;
}
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background-color: #f9f9f9;
border: 1px solid #ddd;
border-radius: 8px;
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max-width: 600px;
margin: 20px auto;
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.calculator-form select {
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padding: 12px;
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border-radius: 5px;
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box-sizing: border-box;
transition: border-color 0.3s ease;
}
.calculator-form input[type="number"]:focus,
.calculator-form select:focus {
border-color: #007bff;
outline: none;
box-shadow: 0 0 5px rgba(0, 123, 255, 0.25);
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margin-top: 25px;
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.calculator-form button:hover {
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transform: translateY(-2px);
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.result-container {
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border-radius: 8px;
padding: 20px;
margin-top: 30px;
text-align: center;
}
.result-container h3 {
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margin-top: 0;
margin-bottom: 15px;
font-size: 1.4em;
}
.gfr-value {
font-size: 2.2em;
font-weight: bold;
color: #28a745; /* Green for good results, can be dynamic */
margin-bottom: 15px;
}
.gfr-interpretation {
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color: #333;
}
.gfr-interpretation strong {
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Understanding GFR and Kidney Health
The Glomerular Filtration Rate (GFR) is the best measure of kidney function. It estimates how much blood passes through the glomeruli (tiny filters in the kidneys) each minute. A healthy GFR means your kidneys are effectively filtering waste products from your blood.
Why is GFR Important?
Monitoring GFR is crucial for detecting and managing Chronic Kidney Disease (CKD). Early detection allows for interventions that can slow the progression of kidney damage and prevent serious complications. The National Kidney Foundation (NKF) recommends regular GFR checks, especially for individuals at higher risk of kidney disease, such as those with diabetes, high blood pressure, heart disease, or a family history of kidney failure.
How the CKD-EPI 2021 Equation Works
This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2021 equation. This formula is widely endorsed by major kidney organizations, including the NKF, because it provides a more accurate GFR estimate than older equations and, importantly, does not include race as a factor. It calculates GFR based on your serum creatinine level (a waste product in your blood), age, and sex.
- Serum Creatinine (mg/dL): A blood test measures the amount of creatinine. Higher levels can indicate reduced kidney function.
- Age (years): Kidney function naturally declines with age.
- Sex: Biological sex influences muscle mass and creatinine production, which are factored into the equation.
Interpreting Your GFR Results (GFR Stages):
GFR values are categorized into stages to help understand the severity of kidney disease:
- Stage 1: GFR ≥ 90 mL/min/1.73m² – Normal or high GFR. Kidneys are functioning well.
- Stage 2: GFR 60-89 mL/min/1.73m² – Mildly decreased GFR. May indicate early kidney damage.
- Stage 3a: GFR 45-59 mL/min/1.73m² – Mild-to-moderately decreased GFR.
- Stage 3b: GFR 30-44 mL/min/1.73m² – Moderately-to-severely decreased GFR.
- Stage 4: GFR 15-29 mL/min/1.73m² – Severely decreased GFR. Significant kidney damage.
- Stage 5: GFR < 15 mL/min/1.73m² – Kidney failure. Requires dialysis or kidney transplant.
It's important to remember that a single GFR reading doesn't tell the whole story. Your doctor will consider your overall health, other test results, and medical history to make a diagnosis and recommend a treatment plan.
Example Calculation:
Let's consider an example:
- Serum Creatinine: 0.9 mg/dL
- Age: 45 years
- Sex: Female
Using the CKD-EPI 2021 equation, the estimated GFR would be approximately 85.23 mL/min/1.73m². This falls into Stage 2, indicating mildly decreased GFR. A doctor would then assess if there are other signs of kidney damage.
Another example:
- Serum Creatinine: 1.5 mg/dL
- Age: 60 years
- Sex: Male
The estimated GFR would be approximately 50.17 mL/min/1.73m². This falls into Stage 3a, indicating mild-to-moderately decreased GFR, warranting further investigation and management.
Always consult with a healthcare professional for accurate diagnosis and personalized medical advice regarding your kidney health.