Glomerular Filtration Rate Calculator

Glomerular Filtration Rate (GFR) Calculator

function calculateGFR() { var serumCreatinine = parseFloat(document.getElementById('serumCreatinine').value); var age = parseInt(document.getElementById('age').value); var sexMale = document.getElementById('sexMale').checked; var raceBlack = document.getElementById('raceBlack').checked; if (isNaN(serumCreatinine) || serumCreatinine <= 0) { document.getElementById('gfrResult').innerHTML = 'Please enter a valid Serum Creatinine value.'; return; } if (isNaN(age) || age 120) { document.getElementById('gfrResult').innerHTML = 'Please enter a valid Age (18-120 years).'; return; } var kappa, alpha; var sexFactor = 1; var raceFactor = 1; if (sexMale) { kappa = 0.9; alpha = -0.411; } else { // Female kappa = 0.7; alpha = -0.329; sexFactor = 1.018; } if (raceBlack) { raceFactor = 1.159; } var scrOverKappa = serumCreatinine / kappa; var gfr = 141 * Math.pow(Math.min(scrOverKappa, 1), alpha) * Math.pow(Math.max(scrOverKappa, 1), -1.209) * Math.pow(0.993, age) * sexFactor * raceFactor; document.getElementById('gfrResult').innerHTML = '

Estimated GFR: ' + gfr.toFixed(2) + ' mL/min/1.73m²

'; }

Understanding Your Glomerular Filtration Rate (GFR)

The Glomerular Filtration Rate (GFR) is a crucial measure of kidney function. It estimates how much blood passes through the glomeruli each minute. Glomeruli are tiny filters in your kidneys that remove waste products and excess water from your blood. A healthy GFR indicates that your kidneys are effectively cleaning your blood, while a low GFR can signal kidney disease.

Why is GFR Important?

• Early Detection of Kidney Disease: GFR is the best indicator of kidney function and is used to detect kidney disease early, often before symptoms appear.
• Staging Kidney Disease: Healthcare providers use GFR values to classify the stage of chronic kidney disease (CKD), which helps in determining the appropriate treatment and management plan.
• Monitoring Treatment: GFR is monitored over time to assess the effectiveness of treatments and the progression of kidney disease.
• Medication Dosing: Many medications are cleared by the kidneys. GFR helps doctors adjust medication dosages to prevent accumulation and toxicity, especially in individuals with impaired kidney function.

How is GFR Calculated?

Directly measuring GFR is complex and usually involves specialized tests. Therefore, GFR is typically estimated (eGFR) using formulas that incorporate readily available blood test results, primarily serum creatinine, along with demographic factors like age, sex, and sometimes race.

This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) 2009 formula, which is widely recommended for its accuracy across various populations. The formula takes into account:

• Serum Creatinine (mg/dL): Creatinine is a waste product from muscle metabolism. Healthy kidneys filter creatinine efficiently, so higher levels in the blood can indicate reduced kidney function.
• Age (years): Kidney function naturally declines with age.
• Sex: Men and women typically have different muscle mass and creatinine levels, which are accounted for in the formula.
• Race (Black/Non-Black): Historically, GFR formulas included a race coefficient for individuals identified as Black, based on observed differences in average creatinine levels. However, there is an ongoing re-evaluation and movement towards race-neutral GFR equations in clinical practice to address concerns about health equity and potential biases. This calculator includes the race factor as it is part of the original CKD-EPI 2009 formula, but users should be aware of these evolving discussions.

Interpreting Your GFR Results (mL/min/1.73m²)

GFR is reported in milliliters per minute per 1.73 square meters (mL/min/1.73m²), which normalizes the result to an average body surface area.

• GFR 90 or higher: Generally considered normal kidney function.
• GFR 60-89: May indicate early kidney damage, especially if there are other signs of kidney disease (e.g., protein in urine).
• GFR 45-59: Mild to moderate decrease in kidney function (CKD Stage 3a).
• GFR 30-44: Moderate to severe decrease in kidney function (CKD Stage 3b).
• GFR 15-29: Severe decrease in kidney function (CKD Stage 4).
• GFR less than 15: Kidney failure (CKD Stage 5), often requiring dialysis or kidney transplant.

Examples:

1. Example 1: Healthy Adult Male
   • Serum Creatinine: 1.0 mg/dL
   • Age: 40 years
   • Sex: Male
   • Race: Non-Black
   • Calculated GFR: Approximately 95 mL/min/1.73m² (Normal kidney function)
2. Example 2: Older Adult Female with Mild Impairment
   • Serum Creatinine: 0.8 mg/dL
   • Age: 65 years
   • Sex: Female
   • Race: Non-Black
   • Calculated GFR: Approximately 70 mL/min/1.73m² (May indicate early kidney damage, warrants monitoring)
3. Example 3: Adult Black Male with Moderate Impairment
   • Serum Creatinine: 1.5 mg/dL
   • Age: 55 years
   • Sex: Male
   • Race: Black
   • Calculated GFR: Approximately 62 mL/min/1.73m² (Borderline normal to early kidney damage, warrants further investigation)

Disclaimer: This calculator provides an estimated GFR based on the CKD-EPI 2009 formula and should be used for informational purposes only. It is not 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.