Key takeaways
Three things to remember
- 01
eGFR estimates how much blood your kidneys filter per minute, calculated from blood creatinine plus age and sex, with 90 or above considered normal.
- 02
Muscle mass, creatine supplements, hard workouts, and dehydration can lower eGFR without kidney damage, so repeat unexpected results and consider a cystatin C based estimate.
- 03
A value below 60 for 3 months signals chronic kidney disease, and the direction of your trend across tests matters more than any one number.
How it works
The Mechanism
Each kidney contains roughly a million tiny filters called glomeruli. Blood is pushed through them, and waste products slip into urine while blood cells and most protein stay behind. The true filtering rate is hard to measure directly, so labs estimate it instead.
The usual estimate starts with creatinine, a waste product that muscles release at a steady pace. If the kidneys filter well, creatinine is cleared and the blood level stays low. If filtering slows, creatinine builds up. The lab plugs your creatinine, age, and sex into a standard equation (the current standard is a 2021 revision that no longer adjusts for race) and reports the result in mL/min/1.73 m2, a rate scaled to an average body size.
Because the starting point is creatinine, anything that changes creatinine without changing the kidneys can skew the answer. More muscle, creatine supplements, a recent hard workout, or a large cooked-meat meal can push creatinine up and eGFR down. When that is a concern, a second marker called cystatin C, which does not depend on muscle, can be used to build a more accurate estimate.
In practice
Why It Matters
The single most useful number for catching kidney decline years before you would feel anything.
Kidney disease is usually silent until it is advanced, and eGFR is the standard way to catch it early. Doctors use it to stage kidney health, to dose many medications, and to judge the safety of some imaging dyes and anti-inflammatory painkillers. For lifters and anyone taking creatine, knowing how muscle and supplements affect the number prevents both false alarms and missed problems. The trend across several tests tells you more than any single result.
Common misconception
A low eGFR in a muscular person or a creatine user does not automatically mean kidney damage, because creatinine can run high from muscle and supplements alone. The reverse also matters: a normal-looking eGFR does not rule out kidney disease, since protein leaking into urine can appear before the filtering rate drops. That is why a urine albumin test is paired with eGFR, and why an unexpected result is repeated before anyone draws conclusions.
Reference ranges
What a Healthy Range Looks Like
Normal or high
90 or above mL/min/1.73 m2
Healthy filtering if there is no other sign of kidney damage
Mildly decreased
60 to 89 mL/min/1.73 m2
Common with age and often not a concern unless urine tests show damage
Mild to moderately decreased
45 to 59 mL/min/1.73 m2
Counts as chronic kidney disease if it persists for 3 months; worth medical follow-up
Moderately to severely decreased
Below 45 mL/min/1.73 m2
Reduced kidney function that needs active medical management
An eGFR of 90 or above is considered normal for a younger adult, and 60 to 89 is common and often fine as people age. Kidney function drifts down by about 1 mL/min/1.73 m2 per year on average after age 40. A value below 60 for 3 months or more is the usual threshold for chronic kidney disease, and a single low reading should be repeated before it is acted on.
Signs it is disrupted
- Foamy or bubbly urine, which can mean protein is leaking through the filters.
- Swelling in the ankles, feet, or around the eyes from fluid the kidneys are not clearing.
- Needing to urinate noticeably more or less than usual, especially at night.
- Persistent fatigue, itching, or a metallic taste in later stages when waste products build up.
- New or hard-to-control high blood pressure, since kidneys and blood pressure affect each other.
What moves it
How to Improve It
Control blood pressure. Aim to keep readings below about 130/80 mmHg, since high pressure damages the glomeruli over years and is a leading cause of falling eGFR.
Manage blood sugar. Keep fasting glucose under 100 mg/dL and HbA1c under 5.7 percent, because chronically high glucose is the other leading cause of kidney decline.
Limit regular NSAID use. Avoid taking ibuprofen or naproxen on most days; frequent use over weeks reduces blood flow to the kidneys, especially when dehydrated.
Stay hydrated. Drink enough that urine is pale yellow through the day; dehydration briefly raises creatinine and can make a lab result look worse than it is.
Time your blood draw. Skip hard training for 24 hours and avoid a heavy meat meal before a blood draw, and tell your doctor if you take creatine, which can raise creatinine by about 0.1 to 0.3 mg/dL without harming the kidneys.
Add cystatin C. If you are muscular or your result does not fit the rest of your health, ask for an eGFR that includes cystatin C, and pair it with a urine albumin test once a year.
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