The Cockcroft-Gault formula is a widely used method for estimating the Glomerular Filtration Rate (GFR) by calculating Creatinine Clearance (CrCl). Developed in 1973 by Donald W. Cockcroft and M. Gault, this equation helps medical professionals assess kidney function and determine appropriate drug dosages, especially for medications cleared by the renal system.
The Cockcroft-Gault Formula
The standard formula for estimating CrCl is as follows:
Creatinine is a waste product produced by muscle metabolism. The kidneys are responsible for filtering creatinine out of the blood. If kidney function declines, the blood levels of creatinine rise because the kidneys are less efficient at clearing it. By calculating the clearance rate, clinicians can stage Chronic Kidney Disease (CKD) and adjust pharmaceutical prescriptions to avoid toxicity.
Clinical Interpretation of Results
While results vary based on individual health history, general ranges for renal function are often interpreted as:
Normal: Greater than 90 mL/min
Mild Impairment: 60–89 mL/min
Moderate Impairment: 30–59 mL/min
Severe Impairment: 15–29 mL/min
Kidney Failure: Less than 15 mL/min
Example Calculation
Consider a 65-year-old male weighing 80 kg with a serum creatinine of 1.2 mg/dL:
If the patient were female with the same metrics, the result would be 69.44 × 0.85 = 59.02 mL/min.
Limitations of the Formula
The Cockcroft-Gault equation was developed using actual body weight. In obese patients, this may overestimate renal function. In such cases, clinicians might use Adjusted Body Weight or Ideal Body Weight. Additionally, the formula is less accurate in patients with rapidly changing creatinine levels, such as those with acute kidney injury.
function calculateCrCl() {
var sex = document.getElementById("cg-sex").value;
var age = parseFloat(document.getElementById("cg-age").value);
var weight = parseFloat(document.getElementById("cg-weight").value);
var weightUnit = document.getElementById("cg-weight-unit").value;
var creatinine = parseFloat(document.getElementById("cg-creatinine").value);
var creatinineUnit = document.getElementById("cg-creatinine-unit").value;
var resultBox = document.getElementById("cg-result-box");
var resultDisplay = document.getElementById("cg-value");
if (isNaN(age) || isNaN(weight) || isNaN(creatinine) || age <= 0 || weight <= 0 || creatinine <= 0) {
alert("Please enter valid positive numbers for all fields.");
return;
}
// Convert weight to kg if in lbs
var finalWeight = weight;
if (weightUnit === "lbs") {
finalWeight = weight / 2.20462;
}
// Convert creatinine to mg/dL if in umol/L
var finalCreatinine = creatinine;
if (creatinineUnit === "umol") {
finalCreatinine = creatinine / 88.4;
}
// Formula: ((140 – age) * weight) / (72 * creatinine)
var crcl = ((140 – age) * finalWeight) / (72 * finalCreatinine);
// Apply gender multiplier
if (sex === "female") {
crcl = crcl * 0.85;
}
resultDisplay.innerHTML = crcl.toFixed(2) + " mL/min";
resultBox.style.display = "block";
}