function calculateEGFR() {
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var creatinine = parseFloat(document.getElementById('creatinine').value);
var resultBox = document.getElementById('resultBox');
var gfrDisplay = document.getElementById('gfrValue');
var stageDisplay = document.getElementById('stageInfo');
var interpretationDisplay = document.getElementById('interpretation');
// Validation
if (isNaN(age) || isNaN(creatinine) || age <= 0 || creatinine <= 0) {
alert("Please enter valid positive numbers for Age and Creatinine.");
return;
}
// CKD-EPI 2021 Constants
var kappa = (gender === 'female') ? 0.7 : 0.9;
var alpha = (gender === 'female') ? -0.241 : -0.302;
var genderFactor = (gender === 'female') ? 1.012 : 1.0;
// Calculation Steps
// Formula: 142 * min(Scr/k, 1)^alpha * max(Scr/k, 1)^-1.200 * 0.9938^Age * GenderFactor
var scrOverKappa = creatinine / kappa;
var minPart = Math.min(scrOverKappa, 1);
var maxPart = Math.max(scrOverKappa, 1);
var eGFR = 142 * Math.pow(minPart, alpha) * Math.pow(maxPart, -1.200) * Math.pow(0.9938, age) * genderFactor;
// Rounding
eGFR = Math.round(eGFR);
// Display Results
resultBox.style.display = 'block';
gfrDisplay.innerHTML = eGFR + ' mL/min/1.73m²';
// Determine Stage and Formatting
var stageText = "";
var stageClass = "";
var interpText = "";
if (eGFR >= 90) {
stageText = "Stage G1: Normal or High Function";
stageClass = "stage-normal";
interpText = "Your kidneys are functioning normally. However, other signs of kidney damage could still be present.";
} else if (eGFR >= 60) {
stageText = "Stage G2: Mildly Decreased";
stageClass = "stage-normal"; // Still considered acceptable generally unless other markers exist
interpText = "Your kidney function is slightly reduced but may be considered normal for older adults.";
} else if (eGFR >= 45) {
stageText = "Stage G3a: Mild to Moderate Decrease";
stageClass = "stage-warning";
interpText = "This indicates mild to moderate loss of kidney function.";
} else if (eGFR >= 30) {
stageText = "Stage G3b: Moderate to Severe Decrease";
stageClass = "stage-warning";
interpText = "This indicates moderate to severe loss of kidney function. Medical consultation is recommended.";
} else if (eGFR >= 15) {
stageText = "Stage G4: Severely Decreased";
stageClass = "stage-danger";
interpText = "Severe reduction in kidney function. Preparation for kidney replacement therapy may be needed.";
} else {
stageText = "Stage G5: Kidney Failure";
stageClass = "stage-danger";
interpText = "This level indicates kidney failure (end-stage renal disease). Immediate medical attention is required.";
}
stageDisplay.className = "stage-indicator " + stageClass;
stageDisplay.innerHTML = stageText;
interpretationDisplay.innerHTML = interpText;
}
Understanding Creatinine and Calculated Glomerular Filtration Rate (eGFR)
The relationship between creatinine levels and the Calculated Glomerular Filtration Rate (eGFR) is fundamental to diagnosing and monitoring kidney health. This tool helps interpret blood test results by using the CKD-EPI 2021 equation, which is the current standard recommended by the National Kidney Foundation.
What is Serum Creatinine?
Creatinine is a chemical waste product generated from muscle metabolism. It is produced at a relatively constant rate by the body and is filtered out of the blood almost entirely by the kidneys. Because of this, the level of creatinine in your blood (Serum Creatinine) is a reliable indicator of how well your kidneys are filtering waste.
Typical Ranges:
Men: 0.7 to 1.3 mg/dL
Women: 0.6 to 1.1 mg/dL
When kidney function declines, creatinine accumulates in the blood, causing these levels to rise. However, creatinine alone isn't a perfect measure because it can be influenced by muscle mass, diet, and age. This is why we calculate eGFR.
What is eGFR?
eGFR stands for estimated Glomerular Filtration Rate. It is a mathematical calculation that estimates the flow rate of filtered fluid through the kidney. It is considered the best test to measure your level of kidney function and determine your stage of kidney disease.
Unlike a simple creatinine test, the eGFR calculation accounts for variables like age and gender to provide a more accurate picture of kidney health.
Interpreting Your eGFR Result
The eGFR number roughly represents the percentage of kidney function remaining. A value of 100 means your kidneys are working at 100% capacity (though values above 90 are considered normal).
CKD Stage
eGFR Range
Description
Stage 1
90 or higher
Normal or high kidney function (damage may be present)
Stage 2
60 – 89
Mildly decreased kidney function
Stage 3a
45 – 59
Mild to moderately decreased function
Stage 3b
30 – 44
Moderately to severely decreased function
Stage 4
15 – 29
Severely decreased kidney function
Stage 5
Below 15
Kidney failure (End-Stage Renal Disease)
The CKD-EPI 2021 Equation
This calculator uses the CKD-EPI 2021 creatinine equation. This updated formula was developed to provide accurate estimates without including a coefficient for race, which was present in older formulas (like MDRD or CKD-EPI 2009). This change ensures more equitable diagnosis and treatment across different populations.
When Should You See a Doctor?
An eGFR below 60 for three months or more is a key indicator of Chronic Kidney Disease (CKD). However, a single lower result can be caused by dehydration or other temporary factors. Conversely, an eGFR above 60 doesn't guarantee perfect health if there are other signs of damage, such as protein in the urine.
Always consult a healthcare professional to interpret your specific results in the context of your overall medical history.