How to Calculate Glomerular Filtration Rate Formula
by
Understanding and Calculating Glomerular Filtration Rate (GFR)
The Glomerular Filtration Rate (GFR) is a key indicator of kidney function. It measures how much blood passes through the glomeruli each minute. The glomeruli are tiny filters in your kidneys that remove waste products from your blood. A healthy GFR means your kidneys are effectively filtering waste. A low GFR can indicate kidney disease.
Several formulas can be used to estimate GFR, as directly measuring it is complex. The most common formulas are based on serum creatinine levels, along with factors like age, sex, and race. While race was historically included in some formulas (like the Cockcroft-Gault equation and the MDRD study equation), current guidelines often recommend using race-neutral equations to avoid potential bias. The CKD-EPI equation is widely adopted and considered more accurate.
Here, we will use the CKD-EPI 2021 creatinine equation, which is recommended by the KDIGO guidelines. This equation is:
For males: GFR = 146 × (serum creatinine/0.993)^-1.154 × 0.993^age
For females: GFR = 146 × (serum creatinine/0.993)^-1.154 × 0.993^age × 1.018
Let's break down the inputs needed for this calculation:
* **Serum Creatinine:** This is a blood test that measures the amount of creatinine, a waste product from muscle activity, in your blood. Higher levels often suggest poorer kidney function. It's typically measured in mg/dL.
* **Age:** Your age in years.
* **Sex:** Whether you are male or female.
—
GFR Calculator (CKD-EPI 2021 Creatinine Equation)
Male
Female
function calculateGFR() {
var serumCreatinine = parseFloat(document.getElementById("serumCreatinine").value);
var age = parseInt(document.getElementById("age").value);
var sex = document.getElementById("sex").value;
var gfrResultElement = document.getElementById("gfrResult");
gfrResultElement.innerHTML = ""; // Clear previous results
if (isNaN(serumCreatinine) || isNaN(age) || serumCreatinine <= 0 || age <= 0) {
gfrResultElement.innerHTML = "Please enter valid positive numbers for Serum Creatinine and Age.";
return;
}
var multiplier = 1;
if (sex === "female") {
multiplier = 1.018;
}
// CKD-EPI 2021 creatinine equation
var gfr = 146 * Math.pow((serumCreatinine / 0.993), -1.154) * Math.pow(0.993, age) * multiplier;
// Ensure GFR is not negative (though unlikely with valid inputs)
if (gfr < 0) {
gfr = 0;
}
gfrResultElement.innerHTML = "Estimated GFR: " + gfr.toFixed(2) + " mL/min/1.73 m²";
}
—
Interpreting Your GFR Results
* **Normal GFR:** A GFR of 90 or higher is generally considered normal.
* **Mildly Decreased GFR (Stage 2 CKD):** A GFR between 60 and 89, especially if present for three months or more and with other signs of kidney damage (like protein in the urine), may indicate Stage 2 Chronic Kidney Disease (CKD).
* **Moderately Decreased GFR (Stage 3 CKD):** A GFR between 30 and 59 indicates moderate kidney damage.
* **Severely Decreased GFR (Stage 4 CKD):** A GFR between 15 and 29 indicates severe kidney damage.
* **Kidney Failure (Stage 5 CKD):** A GFR below 15 indicates kidney failure, often requiring dialysis or a kidney transplant.
It's crucial to discuss your GFR results with your healthcare provider. They can interpret the results in the context of your overall health, medical history, and other diagnostic tests to determine the best course of action.