Creatinine and Calculated Glomerular Filtration Rate

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Estimated Glomerular Filtration Rate (eGFR)

function calculateGFR() { var serumCreatinine = parseFloat(document.getElementById("serumCreatinine").value); var age = parseInt(document.getElementById("age").value); var gender = document.getElementById("gender").value; var race = document.getElementById("race").value; var eGFR = 0; var interpretation = ""; if (isNaN(serumCreatinine) || isNaN(age) || serumCreatinine <= 0 || age <= 0) { document.getElementById("eGFRValue").innerHTML = "Please enter valid positive numbers for all fields."; document.getElementById("interpretation").innerHTML = ""; return; } // CKD-EPI 2021 Equation var raceFactor = 1; if (race === "african_american") { raceFactor = 1.159; } if (gender === "male") { eGFR = 141 * Math.pow(serumCreatinine / 0.97, -1.209) * Math.pow(Math.max(1, age / 108), -0.207); } else { // female eGFR = 144 * Math.pow(serumCreatinine / 0.70, -1.209) * Math.pow(Math.max(1, age / 108), -0.207); } eGFR *= raceFactor; eGFR = Math.round(eGFR); if (eGFR = 15 && eGFR = 30 && eGFR = 60 && eGFR <= 89) { interpretation = "Mild decrease in kidney function (Stage 2 CKD)"; } else { interpretation = "Normal kidney function (Stage 1 CKD)"; } document.getElementById("eGFRValue").innerHTML = "eGFR: " + eGFR + " mL/min/1.73m²"; document.getElementById("interpretation").innerHTML = "Interpretation: " + interpretation; }

Understanding Creatinine and Calculated Glomerular Filtration Rate (eGFR)

The kidneys are vital organs responsible for filtering waste products and excess fluid from your blood, which are then excreted in your urine. Glomerular Filtration Rate (GFR) is a measure of how well your kidneys are performing this filtering function. A higher GFR generally indicates better kidney function.

What is Creatinine?

Creatinine is a waste product produced by normal muscle metabolism. It is released into the bloodstream, filtered by the kidneys, and excreted in the urine. When kidney function declines, the kidneys are less efficient at filtering creatinine, leading to higher levels in the blood.

What is Glomerular Filtration Rate (GFR)?**

The GFR represents the volume of fluid that is filtered from the glomerular capillaries into Bowman's capsule per unit of time. It is considered the best overall index of kidney function. Measuring GFR directly can be complex and involves the injection of specific substances that are filtered but not reabsorbed or secreted by the kidneys. Therefore, in clinical practice, an estimated GFR (eGFR) is commonly calculated using a formula that incorporates serum creatinine levels, age, sex, and race.

The eGFR Calculator Explained

The calculator above uses the CKD-EPI 2021 (Chronic Kidney Disease Epidemiology Collaboration) equation, which is a widely accepted and accurate method for estimating GFR. Here's a breakdown of the inputs:

  • Serum Creatinine (mg/dL): This is the level of creatinine measured in your blood. Higher levels often suggest reduced kidney function.
  • Age (years): Kidney function naturally tends to decline with age.
  • Gender: Biological differences between males and females can influence creatinine production and therefore affect the eGFR calculation.
  • Race: The CKD-EPI equation historically included a race coefficient, as certain populations showed differences in creatinine metabolism. While this is a subject of ongoing discussion and refinement in medical practice, it is still included in this standard equation.

Interpreting Your eGFR Results

The calculated eGFR is reported in milliliters per minute per 1.73 square meters (mL/min/1.73m²). This unit normalizes for body surface area, allowing for comparison between individuals. The results are typically categorized into stages of Chronic Kidney Disease (CKD):

  • Stage 1: eGFR of 90 or higher (with kidney damage)
  • Stage 2: eGFR of 60-89 (with kidney damage)
  • Stage 3a: eGFR of 45-59
  • Stage 3b: eGFR of 30-44
  • Stage 4: eGFR of 15-29
  • Stage 5: eGFR of less than 15 (kidney failure)

It's important to note that a lower eGFR does not always mean you have CKD. Factors like muscle mass, diet, and certain medications can affect serum creatinine levels. A persistently low eGFR, especially when accompanied by other signs of kidney damage (like protein in the urine), is indicative of CKD. Always discuss your eGFR results with your healthcare provider for an accurate diagnosis and management plan.

Example Calculation

Let's consider an example: A 65-year-old African American male has a serum creatinine of 1.2 mg/dL. His age is 65, and he is male and of African American race.

Using the CKD-EPI 2021 equation:

(This is a simplified representation, the calculator performs the exact computation)

The calculator would input these values and compute an eGFR. For this individual, the calculated eGFR might be around 75 mL/min/1.73m², which typically falls into Stage 2 CKD if there are other indicators of kidney damage, or suggests mild kidney function decline.

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