GFR Calculator

Glomerular Filtration Rate Calculator

The glomerular filtration rate (GFR) is a critical measure of kidney function, reflecting how effectively the kidneys filter waste from the blood. Expressed in milliliters per minute per 1.73 square meters of body surface area, GFR indicates the volume of fluid filtered through the glomeruli, the tiny structures in the kidneys responsible for blood purification. Healthy kidneys maintain a high GFR, typically ranging from 100–130 mL/min/1.73m² in men and 90–120 mL/min/1.73m² in women under 40, though these values naturally decline with age. Monitoring GFR is essential for detecting kidney issues early, as a significant drop can signal impaired renal function, potentially progressing to chronic kidney disease (CKD) if untreated.

GFR assessment helps clinicians diagnose and manage kidney health, guiding treatment to prevent complications like dialysis. While a GFR above 60 mL/min/1.73m² is generally adequate, a decline from previous levels or the presence of kidney damage markers, such as proteinuria, may indicate early CKD. The gold standard for measuring GFR, inulin clearance, is highly accurate but impractical for routine use due to its complexity. Instead, formulas estimating GFR from serum creatinine levels—adjusted for factors like age, sex, and muscle mass—are widely used for their simplicity, despite minor inaccuracies. These estimates categorize kidney function into stages, from normal to severe CKD, enabling tailored interventions.

Understanding GFR empowers individuals and healthcare providers to prioritize kidney health. Early detection through GFR monitoring can lead to timely lifestyle changes or treatments, significantly improving outcomes. As kidney disease often progresses silently, regular GFR evaluation is a vital tool for maintaining overall health and preventing long-term complications.

What is GFR?

The glomerular filtration rate (GFR) quantifies how efficiently the kidneys filter blood, serving as a key indicator of renal health. A higher GFR typically reflects better kidney performance, while a significant drop suggests impaired kidney function, leading to reduced filtration over time. For adults under 40, normal GFR ranges, adjusted for body surface area, are approximately 100–130 mL/min/1.73m² for men and 90–120 mL/min/1.73m² for women. After age 40, GFR naturally declines with age. Below is a table showing average estimated GFR values across different age groups.

Average GFR by Age Group

Stages of Chronic Kidney Disease (CKD)

A GFR above 60 mL/min/1.73m² is generally sufficient for most individuals and does not automatically indicate chronic kidney disease (CKD). However, a notable decrease from a previous GFR measurement may signal early kidney issues. Early detection and treatment of kidney disease can significantly reduce the likelihood of requiring dialysis. The table below outlines GFR ranges for CKD stages, which also consider additional factors like proteinuria or kidney damage.

How GFR is Measured

The gold standard for measuring GFR is inulin clearance, which tracks how quickly the kidneys remove inulin—a substance freely filtered without being metabolized, secreted, or reabsorbed. This method, while precise, involves continuous IV infusion, multiple blood and urine samples, and precise timing, making it impractical for routine use. Instead, GFR is often estimated using formulas based on serum creatinine levels, which are simpler to measure but influenced by factors like muscle mass. Higher muscle mass elevates serum creatinine, which can skew GFR estimates. Additionally, small amounts of creatinine are secreted, causing GFR estimates to be overestimated by 10–20%. Despite these limitations, creatinine-based estimates are widely used due to their practicality.

Common GFR Estimation Formulas

Below are three commonly used formulas to estimate GFR based on serum creatinine (SCr, measured in mg/dL), adjusted for factors like age, sex, and race.

IDMS-Traceable MDRD Equation

GFR = 175 × (SCr)^-1.154 × (age)^-0.203 × (0.742 if female) × (1.212 if Black)

CKD-EPI Formula

Black Female

If SCr ≤ 0.7:

GFR = 166 × (SCr/0.7)^-0.329 × 0.993^age

If SCr > 0.7:

GFR = 166 × (SCr/0.7)^-1.209 × 0.993^age

Black Male

If SCr ≤ 0.9:

GFR = 163 × (SCr/0.9)^-0.411 × 0.993^age

If SCr > 0.9:

GFR = 163 × (SCr/0.9)^-1.209 × 0.993^age

Non-Black Female

If SCr ≤ 0.7:

GFR = 144 × (SCr/0.7)^-0.329 × 0.993^age

If SCr > 0.7:

GFR = 144 × (SCr/0.7)^-1.209 × 0.993^age

Non-Black Male

If SCr ≤ 0.9:

GFR = 141 × (SCr/0.9)^-0.411 × 0.993^age

If SCr > 0.9:

GFR = 141 × (SCr/0.9)^-1.209 × 0.993^age

1. Mayo Quadratic Formula

• If SCr < 0.8 mg/dL, use 0.8 mg/dL for SCr:

  GFR = e^(1.911 + 5.249/SCr - 2.114/SCr² - 0.00686 × age - (0.205 if female))
  

1. Schwartz Formula for Children
2. GFR = 0.413 × height (in cm) / SCr