What is eGFR?
Your kidneys filter about a tenth of a litre of blood every minute through millions of tiny sieves, take waste products and surplus water out of it and give the rest back. That filtration rate is the true measure of how well your kidneys work, but measuring it directly takes a complicated test. So it is estimated: from your creatinine, the muscle waste the kidneys have to filter away at a fixed pace, corrected for your age and your sex, which say how much muscle someone has on average. That is the eGFR, the estimated filtration rate, in millilitres per minute for a body of standard size. Because the estimate rests on creatinine, it inherits everything that affects creatinine. Plenty of muscle mass, a hard training session, a meat meal, dehydration and creatine lift creatinine and lower the eGFR without anything wrong with the kidneys; little muscle does the reverse and presents the kidneys as better than they are. And the formula calculates with an average body: in someone much larger or smaller than average, the estimate is off in the same direction. One value is therefore an estimate with a margin; the trend over several measurements is the real number. Your report shows the eGFR in ml/min/1.73m². Healthy is 60 ml/min/1.73m² or higher, and at a young age usually above 90. With the years it falls by itself, about a point a year after your forties, and a value below 60 ml/min/1.73m² that lasts three months or longer is called reduced kidney function.
Why is eGFR relevant?
Kidneys decline silently. They have so much reserve that you notice nothing of losing half, and symptoms only come when little is left. The eGFR makes that decline visible years earlier, and that is the reason it is calculated with every blood test. High blood pressure, a high blood sugar and atherosclerosis are the biggest damagers, and anyone with one of those three follows the eGFR every year. Visible even earlier is protein in the urine, which often precedes a fall in the eGFR by years in diabetes and high blood pressure. For anyone who is healthy, the eGFR is a number to keep high. The higher within the normal range, the more reserve your kidneys have for later. Blood pressure, blood sugar, weight, smoking and salt are the levers, and anti-inflammatory painkillers such as ibuprofen and naproxen are the pitfall: they pinch the blood vessels in the kidney shut, and with regular use, certainly beside blood pressure medicines or in heat and dehydration, they cost filtering capacity. The eGFR also counts for the dosing of many medicines, because what the kidneys have to excrete builds up when they filter less. For anyone who does sport or has a lot of muscle, the eGFR is a number to read with a pinch of salt. A bodybuilder or a creatine user sees the estimate come out ten to twenty points below their true filtration, and a slight older person sees it too high. In both cases cystatin C, a second measure that does not come from the muscles, is the way to know whether the estimate is right.
eGFR reference ranges
What counts beside the number:
- The creatinine the estimate comes from, and how much muscle you have
- Your earlier values, because a fall of more than a point a year counts more than one low value
- Protein in the urine, which often precedes a fall in the eGFR by years
- Whether you had drunk well, trained hard in the days before or use creatine
- Your blood pressure and your blood sugar, the two biggest damagers of the kidneys
- Which medicines you take, especially anti-inflammatory painkillers and blood pressure medicines, and whether the dose fits your eGFR
The classes above are the international staging, and the limit of 60 is where reduced kidney function begins, provided it lasts three months. At Star-shl the lower bound falls with age, so whether 55 counts as abnormal in a seventy-year-old depends on the lab. One value is an estimate with a margin: muscle mass, dehydration, a hard training session and creatine lower it without a kidney problem, and the trend over the years counts more than one number.
What Dutch labs actually use
These four labs do not agree on what kind of number the eGFR even is. Unilabs and Certe publish a single limit: above 60 is fine. Star-shl publishes a range with an upper bound too, and it falls with age. Clinical Diagnostics publishes no range at all, only classes of severity. On few other blood values do they diverge this far.
42 – 97ml/min/1.73m²
At Star-shl this is normal. Unilabs, Certe and Clinical Diagnostics publish a limit, not a range; they are listed below.
these 1 labs call 42 – 97 ml/min/1.73m² normal. Outside that range these 1 labs call it abnormal.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | All adults | > 60 ml/min/1.73m²Decision limit |
| Star-shl2026 | Men under 50 | 56–95 ml/min/1.73m² |
| Men 50–60 | 52–86 ml/min/1.73m² | |
| Men 60–70 | 41–87 ml/min/1.73m² | |
| Men 70+ | 31–87 ml/min/1.73m² | |
| Women under 50 | 42–97 ml/min/1.73m² | |
| Women 50–60 | 44–86 ml/min/1.73m² | |
| Women 60–70 | 40–95 ml/min/1.73m² | |
| Women 70–80 | 31–83 ml/min/1.73m² | |
| Women 80+ | 38–71 ml/min/1.73m² | |
| Certe2026 | From 18 yrs | > 60 ml/min/1.73m²Decision limit |
| Clinical Diagnostics2026 | High normal or mildly reduced | ≥ 60 ml/min/1.73m²Decision limit |
| Mildly to moderately reduced | 45–59 ml/min/1.73m²Decision limit | |
| Moderately to severely reduced | 30–44 ml/min/1.73m²Decision limit | |
| Severely reduced | 15–29 ml/min/1.73m²Decision limit | |
| Kidney failure | < 15 ml/min/1.73m²Decision limit |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
eGFR high or low: what it means
A low eGFR means your kidneys filter less, or the estimate comes out lower than your true filtration. In order of how often it occurs: reduced kidney function, and then the question belongs with it whether it has been so for three months and whether there is protein in the urine; plenty of muscle mass, which makes more creatinine with healthy kidneys; and dehydration, which lowers it temporarily. After that come a hard training session in the days before, creatine, high blood pressure or diabetes as the damagers in the long term, and medicines that slow the excretion of creatinine or lower filtration itself. Between 45 and 59 ml/min/1.73m² the kidney function is mildly to moderately reduced, between 30 and 44 ml/min/1.73m² moderately to severely, and below 30 ml/min/1.73m² a kidney specialist belongs with it. A high eGFR is no problem in itself, but can present the kidneys as better than they are. Little muscle mass is the most common reason: little creatinine gives a too favourable estimate, especially in older people and after long illness. In pregnancy the kidneys really do filter harder. Rare are hyperfiltration, in which the kidneys temporarily work too hard early in diabetes and that precedes damage, and a severe liver disease, in which the liver no longer makes the raw material of creatinine. A high eGFR in someone with little muscle is a reason to read cystatin C alongside, not to be reassured. What you do about it: with a low value from the circumstances you repeat well hydrated, on a rest day and without creatine. With a low value from the kidneys, blood pressure and blood sugar are the two levers that slow the fall, followed by weight, stopping smoking, less salt and drinking enough. Avoid anti-inflammatory painkillers, and have the dose of every new medicine adjusted to your eGFR. Blood pressure medicines that protect the kidney, and in diabetes drugs that relieve the kidney, are the treatment a doctor starts as soon as the eGFR falls or there is protein in the urine. Always read the eGFR beside the creatinine it comes from and beside your muscle mass, beside protein in the urine, which responds earlier, beside potassium and sodium, which say whether the kidneys are still doing their job, and with doubt beside cystatin C. The trend over the years says more than one value.
What lowers it
Your kidneys filter less, or the estimate comes out lower than your true filtration.
| Cause | How often |
|---|---|
| Reduced kidney functionThe reason this value exists; it only counts as chronic once it lasts three months, and protein in the urine belongs with it | Often |
| Plenty of muscle massMore creatinine with healthy kidneys lowers the estimate; cystatin C shows whether the kidneys really do less | Often |
| DehydrationTemporary, and it recovers as soon as you have drunk well again | Often |
| Hard training shortly before the drawMuscle breakdown yields creatinine and so lowers the estimate for a few days | Sometimes |
| Creatine supplementationRaises the production of creatinine by ten to twenty percent, not the strain on your kidneys | Sometimes |
| High blood pressure or diabetesTogether with atherosclerosis the biggest damagers of the kidneys in the long term; an eGFR falling faster than a point year after year is the signal | Sometimes |
| MedicationSome antibiotics and acid-reducing medicines slow the excretion of creatinine without touching filtration; anti-inflammatory painkillers and blood pressure medicines lower filtration itself | Sometimes |
What raises it
No problem in itself, but the estimate can present the kidneys as better than they are.
| Cause | How often |
|---|---|
| Little muscle massLittle creatinine gives a too favourable estimate, especially in older people and after long illness; cystatin C is then the more honest measure | Often |
| PregnancyBlood flow to the kidney increases and the kidneys really do filter harder; after the birth it is back | Sometimes |
| HyperfiltrationEarly in diabetes the kidneys temporarily work too hard; it precedes damage and is a reason to tackle the blood sugar | Rare |
| Severe liver diseaseThe liver no longer makes the raw material of creatinine, which lifts the estimate while the kidneys can do less than it seems | Rare |
How does an eGFR blood test work?
- Referral
- Not needed. The eGFR is calculated automatically as soon as creatinine is measured, and you can have that done yourself.
- Fasting
- Not strictly needed, but a large portion of meat the evening before lifts creatinine for a few hours and with it lowers the estimate.
- When
- Well hydrated, on a rest day and not in the days after a hard training session. If you want to know your kidney function, stop creatine a few weeks beforehand.
- The draw
- One tube of blood from a vein in your arm; the eGFR is a calculation on the creatinine from it. Ask for protein in the urine alongside if you really want to know your kidneys, and cystatin C if you have a lot or little muscle.
- Repeating
- With a value below 60 after three months, because only then does it count as chronic. With high blood pressure, diabetes or medicines that strain the kidneys every year, and otherwise every few years to know the trend.
- Which test
- eGFR is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is the eGFR?
An estimate of how many millilitres of blood your kidneys clean per minute, calculated from your creatinine, your age and your sex. Measuring it directly takes a complicated test, so the lab calculates it. Because the estimate rests on creatinine, it inherits everything that affects creatinine: muscle mass, dehydration, training and creatine. It is the number your kidney function is read from, and the trend says more than one value.
What is a normal eGFR value?
60 ml/min/1.73m² or higher, and at a young age usually above 90. With the years the value falls by itself, about a point a year after your forties, so a seventy-year-old with a value in the 60s has kidneys that fit their age. Below 60 lasting three months is called reduced kidney function. One value has a margin; the trend over several measurements is the real number.
What does a low or falling eGFR mean?
That your kidneys filter less, or that the estimate comes out lower than your true filtration. Plenty of muscle mass, dehydration, a hard training session and creatine lower the value without a kidney problem; so repeat well hydrated, on a rest day and without creatine. If it stays low, or falls faster than a point a year, it is the kidneys, and then protein in the urine, blood pressure and blood sugar belong with it. Below 30 ml/min/1.73m² a kidney specialist belongs with it.
Is a high eGFR bad?
Not in itself, but it can present the kidneys as better than they are. Little muscle mass gives little creatinine and with it a too favourable estimate, especially in older people and after long illness. In pregnancy the kidneys really do filter harder. Rare is hyperfiltration early in diabetes, in which the kidneys temporarily work too hard before they suffer damage. Anyone with little muscle reads cystatin C alongside.
Why does my eGFR differ per measurement?
Because it is an estimate on a value that moves from day to day. How much you drank, whether you trained the day before, what you ate and whether you use creatine shift creatinine and with it the eGFR by a few points. So measure under the same conditions, and look at the trend over several measurements rather than at one number. A fall of more than a point a year over several years is the signal.
How do I protect my kidneys?
With blood pressure and blood sugar as the two biggest levers, because high blood pressure, diabetes and atherosclerosis are the damagers in the long term. After that weight, stopping smoking, less salt and drinking enough. Go easy on anti-inflammatory painkillers such as ibuprofen and naproxen, which pinch the blood vessels in the kidney shut, certainly beside blood pressure medicines or in heat. And have protein in the urine measured, because that responds years earlier.
Why is there 1.73 in the unit?
Because the estimate is converted to a body of standard size, with a body surface of 1.73 square metres, so that the value of a small woman and a large man can be compared. In someone much larger or smaller than average the estimate is therefore slightly off: too low in a large body, too high in a small one. For the dosing of medicines a pharmacist converts that back where needed.
What is the difference from the eGFR from cystatin C?
The input. The ordinary eGFR comes from creatinine, which comes from your muscles; the other from cystatin C, a protein all cells make and that does not depend on your muscle mass. In a bodybuilder, a creatine user or a slight older person the two diverge, and then the difference says who is right. If they sit close together, they confirm each other.
Which tests include eGFR?
eGFR is in the Biological age test (€69, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Read on
Sources
- 1.KDIGO, Clinical Practice Guideline for the Evaluation and Management of CKD. 2024. kdigo.org
- 2.Unilabs, test catalogue (Dutch): eGFR (CKD-EPI). 2026. bepalingenklapper.nl
- 3.Star-shl, test catalogue (Dutch): eGFR. 2026. star-shl.nl
- 4.Certe, test catalogue (Dutch): eGFR (CKD-EPI). 2026. bepalingenwijzer.certe.nl
- 5.Clinical Diagnostics, lab guide (Dutch): creatinine and CKD-EPI. 2026. clinicaldiagnostics.nl
- 6.NHG guideline on chronic kidney disease (M109), Dutch College of General Practitioners. 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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