Glomerular filtration rate (GFR)

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Serum creatinine: (umol/L)
 
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What is Glomerular Filtration Rate (GFR)?

Glomerular Filtration Rate (GFR) is a measure of how well the kidneys are functioning, specifically how efficiently they filter waste and excess fluids from the blood. It is an important indicator of kidney health and is used to assess the stage of kidney disease. The GFR tells healthcare providers how much blood the kidneys filter per minute, and is usually measured in milliliters per minute (mL/min).

The GFR is influenced by factors such as age, sex, race, weight, and creatinine levels (a waste product in the blood). A normal GFR for a healthy adult is typically 90 mL/min/1.73 m² or higher.

Why is Glomerular Filtration Rate (GFR) important?

GFR is a key indicator of kidney function, and it is used for:

  1. Diagnosing kidney disease: GFR helps identify kidney damage or kidney disease (such as chronic kidney disease (CKD)). A low GFR indicates impaired kidney function.
  2. Staging kidney disease: GFR helps determine the severity of kidney disease. CKD is classified into five stages based on GFR:
    • Stage 1: Normal or high GFR (90 mL/min or above)
    • Stage 2: Mild decrease in GFR (60-89 mL/min)
    • Stage 3: Moderate decrease in GFR (30-59 mL/min)
    • Stage 4: Severe decrease in GFR (15-29 mL/min)
    • Stage 5: Kidney failure (GFR below 15 mL/min)
  3. Monitoring kidney health: GFR is used to track the progression of kidney disease, especially in people with conditions like diabetes, hypertension, or a history of kidney problems.
  4. Guiding treatment decisions: Doctors may use GFR to determine the need for treatments such as dialysis or kidney transplantation.

How is Glomerular Filtration Rate (GFR) measured?

GFR is typically estimated using blood tests to measure serum creatinine levels. However, more precise tests can be done in clinical settings. The most common method for estimating GFR is through formulas that account for factors like age, sex, and serum creatinine. One common formula is the Modification of Diet in Renal Disease (MDRD) equation, or the CKD-EPI equation.

Here’s how GFR is generally calculated:

  • Serum creatinine levels: The amount of creatinine in the blood is used as an indirect measure of kidney function. The kidneys normally filter creatinine, so high levels suggest kidney dysfunction.
  • Demographic factors: The GFR calculation often factors in age, sex, and race (since GFR can vary among different populations).
  • Body surface area (BSA): The GFR is often adjusted for BSA to give a more accurate estimate of kidney function, since body size can impact kidney function.

In some cases, a 24-hour urine collection might be used to measure the actual amount of creatinine filtered by the kidneys, providing a more accurate measurement of GFR.

When is Glomerular Filtration Rate (GFR) measured?

GFR is measured when:

  1. Kidney disease monitoring: If someone has conditions that affect the kidneys, such as diabetes, high blood pressure, or a family history of kidney disease, doctors may monitor GFR regularly.
  2. Diagnosis of kidney problems: If symptoms like swelling, fatigue, or changes in urine output occur, GFR can help determine if kidney function is impaired.
  3. Routine health checkups: For individuals at high risk for kidney disease (older adults, those with diabetes, or hypertension), GFR might be checked during routine checkups.
  4. Chronic kidney disease (CKD): When someone is diagnosed with CKD, GFR is used to track the progression and severity of the disease and to guide treatment.
  5. Preparing for dialysis or kidney transplant: In advanced kidney disease (Stage 4 or Stage 5), GFR helps determine if dialysis or kidney transplant is needed.