What is creatinine?
Your muscles store energy in creatine, and every day about two percent of it breaks down into creatinine, a waste product your body uses for nothing. The amount released is fairly constant and depends mainly on how much muscle you have: a muscular man makes more of it than a slight woman, and an older person with little muscle makes little. Your kidneys filter it out of your blood and it leaves your body with the urine. As long as production and removal are in balance, the value in your blood stays stable. That is why creatinine is the most common measure of your kidney function: if the kidneys filter less, it builds up. But the value only rises noticeably once the kidneys have already lost a good part of their capacity, and it says something only if you know how much muscle sits behind it. The same value is normal in a bodybuilder and a sign of kidneys doing less in a slight eighty-year-old. That is why the eGFR is calculated alongside, which converts creatinine with age and sex into an estimate of filtering capacity. Your report shows creatinine in µmol/L. Normal for a man of 19 to 80 years is about 64 to 104 µmol/L and for a woman from age 19 50 to 90 µmol/L, where the labs overlap; above age 80 the upper bound moves up at some of the labs.
Why is creatinine relevant?
Kidney damage does not hurt. The kidneys have so much reserve that you notice nothing of losing half their capacity, and the symptoms, tiredness, itching, holding on to fluid, only come when little is left. Creatinine is the value that makes that silent decline visible, years before you feel anything, and that is the reason it is in almost every blood test. High blood pressure and a high blood sugar are the two biggest damagers of the kidneys, and anyone with either follows their creatinine and eGFR every year. For anyone who does sport, creatinine is interesting for another reason: it says something about your muscle mass. Anyone building muscle sees the value rise slowly over months, and anyone using creatine sees it rise by ten to twenty percent without the kidneys noticing anything, because creatine is the raw material creatinine arises from. That is not a kidney problem, but it makes the eGFR too low in athletes, and it is the reason an athlete reads their creatinine with their muscle mass and their supplements alongside. The other side is just as important. In anyone with little muscle, older people, people who have been ill for long, anyone missing a leg, creatinine sits low while the kidneys are already doing less, and a normal value is no reassurance there. For them cystatin C, a second measure of kidney function that does not come from the muscles, is the better addition.
Creatinine reference ranges
What counts beside the number:
- The eGFR from the same draw, which converts creatinine with age and sex into filtering capacity
- How much muscle you have, because the same value is normal in a bodybuilder and not in a slight eighty-year-old
- Whether you use creatine, trained hard in the days before or ate a lot of meat the evening before
- How much you have drunk, because dehydration lifts the value temporarily
- Which medicines you take, especially anti-inflammatory painkillers, blood pressure medicines and some antibiotics
- Your earlier values, because a rise over the years counts more than one high value
Creatinine is always read together with the eGFR, which converts the number with your age and sex into filtering capacity. Muscle mass, dehydration, creatine, a hard training session and a meat meal affect the value without anything wrong with the kidneys. A value within the band does not rule out reduced kidney function in older people or people with little muscle; for them cystatin C is the more honest measure.
What Dutch labs actually use
The older you are, the further these labs diverge. Unilabs and Star-shl raise the upper bound with age, Certe and Clinical Diagnostics do not. For a man of 25 that limit runs from 104 to 113; for a man of 85, from 104 to 149.
50 – 90µmol/L
Between 46 and 50 and between 90 and 91 it depends on the lab, because each sets its limits on its own method and population. Above 91 every lab calls it abnormal.
every lab calls 50 – 90 µmol/L normal. Between 46 and 50 and between 90 and 91 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Men 13–18 yrs | 48–101 µmol/L |
| Women 13–18 yrs | 46–83 µmol/L | |
| Men 19–50 yrs | 61–113 µmol/L | |
| Men 51–65 yrs | 61–120 µmol/L | |
| Men 66–80 yrs | 62–134 µmol/L | |
| Men 81+ | 65–149 µmol/L | |
| Women 19–50 yrs | 48–91 µmol/L | |
| Women 51–65 yrs | 48–99 µmol/L | |
| Women 66–80 yrs | 48–113 µmol/L | |
| Women 81+ | 49–132 µmol/L | |
| Star-shl2026 | Men 13–18 yrs | 48–101 µmol/L |
| Women 13–18 yrs | 46–83 µmol/L | |
| Men 19–50 yrs | 61–113 µmol/L | |
| Men 51–65 yrs | 61–120 µmol/L | |
| Men 66–80 yrs | 62–134 µmol/L | |
| Men over 80 | 65–149 µmol/L | |
| Women 19–50 yrs | 46–91 µmol/L | |
| Women 51–65 yrs | 48–99 µmol/L | |
| Women 66–80 yrs | 48–113 µmol/L | |
| Women over 80 | 49–132 µmol/L | |
| Certe2026 | Men from 18 yrs | 50–110 µmol/L |
| Women from 18 yrs | 50–90 µmol/L | |
| Clinical Diagnostics2026 | Men | 64–104 µmol/L |
| Women | 49–90 µmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Creatinine high or low: what it means
A low creatinine usually means little muscle mass, and that is rarely a problem in itself. It occurs in slight people, older people and after long illness, and in pregnancy, in which the kidneys filter harder and the blood becomes diluted. Rare are hyperfiltration, in which the kidneys temporarily work too hard early in diabetes, and a severe liver disease, in which the liver no longer makes the raw material creatine. The question with a low creatinine is not whether something is wrong, but whether the eGFR beside it presents the kidney function as better than it is. A high creatinine means your kidneys filter less, or you make more than average. The most common explanation first: reduced kidney function, and then the eGFR belongs with it and the question whether it has been so for three months; plenty of muscle mass; and dehydration, which lifts the value temporarily and recovers with drinking. After that come creatine as a supplement, a hard training session in the days before, medicines that slow excretion or lower filtration, such as some antibiotics, acid-reducing medicines, anti-inflammatory painkillers and blood pressure medicines, and high blood pressure or diabetes as the damagers in the long term. A value that rises on repeat counts more than one high value. What you do about it: with a high value from the draw itself you repeat well hydrated, on a rest day, without a steak the evening before and without creatine in the weeks before. With a high value from the kidneys, blood pressure, blood sugar and weight are the levers that slow the decline, together with stopping smoking, less salt and avoiding anti-inflammatory painkillers such as ibuprofen and naproxen, which put extra strain on the kidneys. With a low creatinine from little muscle, strength training is the answer, and cystatin C the more honest measure for the kidneys. Read creatinine beside the eGFR, which converts the number into filtering capacity, beside potassium and sodium, which show whether the kidneys are still doing their job, and with doubt about your muscle mass beside cystatin C. Protein in the urine often precedes a rise in creatinine by years.
What lowers it
Little production, usually through little muscle, and rarely a problem in itself.
| Cause | How often |
|---|---|
| Little muscle massSlight people, older people and anyone who has been ill for long make little creatinine; the eGFR then comes out too favourable | Often |
| PregnancyThe kidneys filter harder and the blood becomes diluted; the value falls and comes back after the birth | 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 creatine; the value falls while the kidneys can do less than it seems | Rare |
What raises it
The kidneys filter less, or you make more than average.
| Cause | How often |
|---|---|
| Reduced kidney functionThe reason this value exists; the eGFR belongs with it, and it only counts as chronic once it lasts three months | Often |
| Plenty of muscle massMore muscle makes more creatinine with healthy kidneys; the eGFR then estimates the kidney function too low | Often |
| DehydrationTemporary, and it recovers as soon as you have drunk well again | Often |
| Creatine supplementationCreatine is the raw material of creatinine; the value rises by ten to twenty percent without the kidneys being strained | Sometimes |
| Hard training shortly before the drawMuscle breakdown yields creatinine; the value sits higher for a few days | Sometimes |
| MedicationSome antibiotics and acid-reducing medicines slow excretion without touching filtration; anti-inflammatory painkillers and blood pressure medicines lower filtration itself | Sometimes |
| High blood pressure or diabetesThe two biggest damagers of the kidneys in the long term; a creatinine that rises year after year is the signal | Sometimes |
How does a creatinine blood test work?
- Referral
- Not needed. Creatinine is in almost every blood test and you can have it measured yourself; the eGFR is calculated alongside automatically.
- Fasting
- Not strictly needed, but a large portion of meat or fish the evening before lifts the value for a few hours, because cooked meat contains creatinine.
- 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. Potassium, sodium, urea and where needed cystatin C come from the same draw.
- Repeating
- With a high value after two to four weeks under better conditions, and with a persistently high value after three months, because only then does it count as chronic. With high blood pressure or diabetes every year.
- Which test
- Creatinine 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 creatinine?
The waste product of creatine, the energy store in your muscles. Every day about two percent of it breaks down into creatinine, and your kidneys filter it out of your blood. Production depends on how much muscle you have, removal on how well your kidneys filter, and the value in your blood is the balance between the two. That is why creatinine is the most common measure of your kidney function, but only beside your muscle mass.
What is a normal creatinine value?
For a man of 19 to 80 years between 64 and 104 µmol/L and for a woman from age 19 between 50 and 90 µmol/L, where the labs overlap; above age 80 the upper bound moves up at some of the labs. More important than the band is the context: the same value is normal in a bodybuilder and a sign of kidneys doing less in a slight eighty-year-old. The eGFR alongside partly calculates that difference away.
What does a high creatinine mean?
That your kidneys filter less, or that you make more than average. Plenty of muscle mass, dehydration, a hard training session, a steak the evening before and creatine lift the value without anything wrong with the kidneys, and some medicines slow excretion. So repeat well hydrated, on a rest day and without creatine. If the value stays high, or rises over the years, it is the kidneys, and then the eGFR and the question about blood pressure and blood sugar belong with it.
What does a low creatinine mean?
Usually little muscle mass, and that is rarely a problem in itself. It occurs in slight people, older people, after long illness and in pregnancy. The pitfall sits in the eGFR: it calculates with an average muscle mass and presents the kidney function as better than it is with little muscle. Anyone with little muscle reads their kidneys better from cystatin C, which does not come from the muscles.
Does creatine lift my creatinine?
Yes, by about ten to twenty percent, because creatine is the raw material creatinine arises from. More creatine in your muscles means more breakdown into creatinine, and your kidneys notice nothing of it; they simply excrete it. The eGFR therefore comes out too low. If you want to know your kidney function, stop creatine a few weeks beforehand, or read cystatin C alongside.
Why does my creatinine rise after a hard training session?
Because muscle work and muscle damage break down extra creatine, and because after a long effort you are often somewhat dehydrated. The value sits higher for a few days, and then it is back. A steak the evening before does something similar, because cooked meat contains creatinine you absorb. Have blood drawn on a rest day and well hydrated if you want to know your usual level.
How do I protect my kidneys?
With blood pressure and blood sugar as the two biggest levers, because high blood pressure and diabetes 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 put extra strain on the kidneys, certainly together with blood pressure medicines. And have protein in the urine measured, because that often precedes a rise in creatinine by years.
When does a high creatinine count as kidney damage?
When the eGFR repeatedly stays below 60, or when there is protein in the urine, and that lasts three months or longer. One high value after a training session or on a hot day does not count. A value that rises year after year counts more than how high it is at one moment, and the speed of the rise is what a doctor follows.
Which tests include creatinine?
Creatinine is in the Biological age test (€69, also as an add-on for €15), in the comprehensive test (€229) and in .
Related biomarkers
Sources
- 1.Unilabs, test catalogue (Dutch): creatinine. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): creatinine. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): creatinine. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): creatinine and CKD-EPI. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
- 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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