From the Guidelines
A GFR test is the best way to measure kidney function and determine your stage of kidney disease, with a normal GFR typically above 90 mL/min/1.73m², while values below 60 for three months or more indicate chronic kidney disease. The test estimates how much blood passes through the glomeruli, which are tiny filters in your kidneys that remove waste from your blood.
Key Points to Consider
- The test is usually performed through a blood test measuring creatinine levels, which is then used in a formula that accounts for age, sex, race, and body size to calculate your GFR 1.
- Sometimes a 24-hour urine collection or a cystatin C blood test may be used for more accurate results.
- No special preparation is typically needed for the blood test.
- Your doctor may order this test if you have risk factors for kidney disease such as diabetes, high blood pressure, heart disease, or a family history of kidney problems.
- Regular GFR testing is important for those at risk because kidney disease often has no symptoms until significant damage has occurred, and early detection allows for interventions that can slow disease progression 1.
Importance of GFR Testing
- GFR is the best measure of overall kidney function in health and disease 1.
- The normal level of GFR varies according to age, sex, and body size.
- A GFR level less than 60 mL/min per 1.73 m2 represents loss of half or more of the adult level of normal kidney function.
- Below this level, the prevalence of complications of chronic kidney disease increases.
Estimating GFR
- Estimates of GFR are the best overall indices of the level of kidney function 1.
- Physicians should estimate the level of GFR from prediction equations that take into account the serum creatinine concentration and some or all of the following variables: age, sex, race, and body size.
- The Modification of Diet in Renal Disease (MDRD) study and Cockcroft-Gault equations provide useful estimates of GFR in adults.
From the Research
GFR Test on Kidneys
- The Glomerular Filtration Rate (GFR) test is a crucial assessment of kidney function, and it can be estimated using serum creatinine levels 2.
- However, serum creatinine is influenced by various factors such as age, sex, muscle mass, and race, which can lead to inaccurate GFR estimates 2, 3.
- The use of cystatin C as an alternative endogenous marker or performing direct measurement of GFR using an exogenous marker such as iohexol can provide more accurate results 3, 4.
- Clinical scenarios where creatinine-based GFR estimation may be invalid include extreme body composition, black race, disagreement between creatinine- and cystatin C-based estimated GFR, and advanced chronic kidney disease 3.
- Measured GFR (mGFR) is not readily available in many centers, but it is essential for accurate and personalized medicine, especially in patients with complex kidney disease 3, 4.
- The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation and the modification of diet in renal disease equation are commonly used to estimate GFR, but they have limitations and may not be suitable for all populations 5.
- Emerging equations that combine serum creatinine and cystatin C, such as the Chronic Renal Insufficiency Cohort (CRIC) study equation, may provide greater accuracy in CKD diagnosis and staging 5.