eGFR is a measure of how well your kidneys are working. It is often reported automatically when you do a creatinine blood test, as a part of your comprehensive metabolic panel (CMP). Read on to learn more about this marker, what it means when your values are outside of the normal range, and how you can increase your eGFR levels.
What is eGFR?
GFR
Glomerular Filtration Rate (GFR) is the amount of blood filtered every minute by tiny filters in the kidneys called glomeruli. Although it may sound complicated, in essence, it measures how well your kidneys are working [1].
The main job of our kidneys is to remove waste and excess water from the blood. This excess water and waste become urine. Kidneys process about 50 gallons (180 liters) of blood every day to produce about 50 ounces (1.5 liters) of urine. When the filtration rate decreases that means the kidneys are not working well and may mean there is kidney damage [2].
GFR is affected by many factors, such as [1]:
- Time of day
- Dietary protein intake
- Exercise
- Age
- Pregnancy
- Obesity
- High blood sugar (hyperglycemia)
- Antihypertensive drugs (used for reducing high blood pressure)
- Acute and chronic kidney disease
Creatinine-derived eGFR
It is hard to directly measure one’s GFR. Instead, scientists have developed a formula to estimate the value indirectly. It’s called it the eGFR, or estimated Glomerular Filtration Rate. The most widely used eGFR equation was developed in the year 2000 and modified in 2009. It takes into account your age, gender, ethnicity/race, and your creatinine levels [1, 3, 4].
Creatinine is a waste product created from the normal wear and tear of muscles. Kidneys filter (remove) almost all of the creatinine from the blood. Because muscle mass changes little from day to day, creatinine production and disposal rates are fairly constant. When kidney filtration rate decreases, blood levels of creatinine increase. Higher creatinine = impaired kidney function [5, 6, 7].
Many laboratories will automatically report eGFR when creatinine is tested [3]. eGFR often helps in the early detection of kidney dysfunction, which is important to prevent further kidney damage.
Why is eGFR a better measure of kidney function than creatinine, or other kidney-associated markers such as BUN (blood urea nitrogen)? Mainly, because it is more sensitive. BUN and creatinine will not increase above normal until more than 50% of total kidney function is lost [5, 3]!
Limitations and Alternatives
Because creatinine is derived from muscles, conditions that affect them will also affect eGFR (calculated using the most widely used formula). People with wasting disease, obesity, amputees, and paraplegics require alternative ways to obtain eGFR. So do those younger than 18 and pregnant women. For bodybuilders, high muscle mass may lead to an underestimation of eGFR [8].
To address this issue, newer equations have been developed linking eGFR to another marker of kidney function, cystatin C. Unlike creatinine, cystatin C can be found in virtually all tissues. Further, some equations include both cystatin C and creatinine – these are the most accurate ones to date [1, 9, 10, 4].
Finally, there are special equations to calculate eGFR in children that take into account the height/length of the child [11].
eGFR Normal Range
Many different equations can be used to derive an estimated glomerular filtration rate (eGFR). Also, normal GFR will vary among ethnic groups. Some labs will report two values – African American and non-African American. Choose the one that best applies to you [1].
All equations will provide a range of values between 0 and about 140. The lower the value, the less efficiently your kidneys are working.
Normal filtration in young adults is about 90 – 120 mL every minute [1]. However, depending on the laboratory, normal results may be reported as >90 or >60 mL/min/1.73m2 [3].
GFR decreases with age. In those older than 70 years, values below 60 mL/min/1.73 m2 can be normal [12].
High eGFR
A high level is usually not a cause for concern.
High eGFR is normally found in pregnancy [13].
Low eGFR
When other factors (such as age and obesity) are excluded, a reduced eGFR indicates impaired kidney function. It can point to a largely reversible acute kidney injury or to a chronic kidney disease that is often irreversible and persistent. Doctors will interpret this test, taking into account a patient’s medical history, symptoms, and other test results.
Chronic kidney disease measured by eGFR has the following stages:
- Stage 1: normal, eGFR: > 90 ml/minute
- Stage 2: mild CKD, eGFR: 60 – 89 ml/minute
- Stage 3: moderate CKD, eGFR: 30 – 59 ml/minute (30 – 60% of kidney function intact)
- Stage 4: severe CKD, eGFR: 15 – 29 ml/minute (15 – 30% of kidney function intact)
- Stage 5: kidney failure, eGFR < 15 ml/minute (less than 15% of kidney function intact)
However, for values in the range of 60 – 89 mL/min/1.73 m2, doctors will consider kidney disease only if there is additional evidence of kidney damage, such as polycystic kidney disease (cysts in the kidneys), proteinuria (protein in the urine), or hematuria (blood in the urine). If there are no such abnormalities, GFR of > 60 mL/min/1.73m2 is regarded as normal [3].
Levels that stay below 60 mL/min/1.73m2 for longer than 3 months are a good indicator of chronic kidney disease. If your eGFR was below 60, talk to your doctor as soon as you can! Your doctor may suggest further testing (blood, urine, or imaging tests).
These factors can decrease eGFR:
- Eating cooked meat before the test [14] – this increases creatinine levels in the blood
- Starvation and long fasting periods [8]
- Bodybuilding and creatine supplementation [15]
- Other factors that can increase creatinine in the blood, such as dehydration [16]
- Medication, including NSAIDs and ACE inhibitors (or angiotensin receptor blockers) [2]
These increase your risk of chronic kidney disease:
- High blood pressure [17, 18]
- Diabetes [19, 20]
- Heart disease [21]
- Obesity [18]
- Smoking [18, 22]
- A family history of kidney disease [18]
- Age (being 60 years old and above) [18]
- Previous kidney injury [18]
- Being born premature/with low birth weight [23, 18]
How to Increase eGFR
The most important thing is to work with a doctor to find out what’s causing your low eGFR and to treat any underlying conditions.
Other than that, to improve your kidney function (and as a result, your eGFR levels):
- Make sure your blood pressure is in the healthy range (around 120/80) [17, 18]
- Aim for a healthy weight [18, 24]
- Eat a lot of fruits and vegetables [25]
- Quit or reduce smoking [18, 22, 26]
- Exercise for at least 30 minutes several times per week [27, 28, 29, 30]
- Control your blood sugar levels if you have diabetes [19, 20]
