What is urea?
Every day your body breaks down protein, from your food and from your own tissue being renewed. That releases nitrogen in the form of ammonia, which is toxic. Your liver turns it into urea, a harmless, readily soluble substance that travels through the blood to the kidneys and leaves the body in the urine. Urea is therefore not a poison but the solution to one, and the value in your blood is the balance of production in the liver and removal by the kidneys. That balance moves with more than your kidneys alone. Anyone who eats a lot of protein makes more urea. Anyone who drinks little holds on to more of it, because with little fluid the kidneys take back water and urea together. That is why urea can rise while nothing is wrong with your kidneys, and that is exactly the difference with creatinine, which mainly follows filtration. Your report shows urea in mmol/L. More than for most values, the range differs per lab, mainly over whether the upper limit rises with age: for an adult it sits between about 6.4 and 8.6 mmol/L, and at one lab it runs on past eighty to 14.2. So compare your value with the range on your own report.
Why is urea relevant?
Urea is the kidney value that tells you something about your day: how much protein you ate and how much you drank. That makes it unreliable as a kidney value and informative as a lifestyle value. A high urea with a normal creatinine is almost always too little fluid or plenty of protein, and it is one of the few results you can read with a glass of water in your hand. For anyone who exercises a lot and eats a lot of protein, that is worth knowing. A protein-rich diet, strength training and protein shakes lift urea without harming healthy kidneys; the number only shows that more nitrogen is being cleared. A low urea, conversely, goes with little protein, and sometimes with a plant-based pattern that runs on the lean side. Where it really is about the kidneys, urea joins in as the second voice beside creatinine and eGFR. With a genuinely reduced kidney function all three rise. In general practice kidney damage is diagnosed on eGFR and on protein in the urine, not on urea; the number is a supplement, not a diagnosis. In advanced kidney disease it is the substance that causes the symptoms, and then it is followed closely.
What Dutch labs actually use
On urea the laboratories differ less about the lower limit than about whether age counts. All three report in mmol/L. For an adult, Unilabs sets the upper limit at 6.4 up to age sixty, Clinical Diagnostics at 7.2 with no age split, and Star-shl at 8.6 for a man aged nineteen to fifty. Star-shl also bands far more finely: in men over eighty the upper limit runs to 14.2. A man of 65 with a urea of 8.0 is raised at Unilabs and Clinical Diagnostics and simply within range at Star-shl.
2.8 – 6.4mmol/L
Between 2.5 and 2.8 and between 6.4 and 7.2 it depends on the lab, because each sets its limits on its own method and population. Above 7.2 every lab calls it abnormal.
every lab calls 2.8 – 6.4 mmol/L normal. Between 2.5 and 2.8 and between 6.4 and 7.2 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | 18-60 jaar | 2,5-6,4 mmol/L |
| Boven 60 jaar | 2,9-7,5 mmol/L | |
| Star-shl2026 | Man 19 t/m 50 jaar | 2,9-8,6 mmol/L |
| Vrouw 19 t/m 50 jaar | 2,5-7,0 mmol/L | |
| Man 51 t/m 65 jaar | 3,2-9,8 mmol/L | |
| Vrouw 51 t/m 65 jaar | 2,9-9,4 mmol/L | |
| Man 66 t/m 80 jaar | 3,6-11,8 mmol/L | |
| Vrouw 66 t/m 80 jaar | 3,1-11,8 mmol/L | |
| Man boven 80 jaar | 4,3-14,2 mmol/L | |
| Vrouw boven 80 jaar | 3,6-13,9 mmol/L | |
| Clinical Diagnostics2026 | Volwassene | 2,8-7,2 mmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Urea high or low: what it means
A high urea comes, in order of how often it occurs, from drinking too little or losing fluid, in heat, exercise, diarrhoea or fever; from eating a lot of protein; and from slower kidney function. Then from anything that breaks down your own tissue: heavy training, fever, prednisone, and prolonged fasting, in which the body draws on muscle. Bleeding in the stomach or gut raises it too, because the blood is digested as protein. A low urea is usually harmless: little protein in the diet or drinking plenty. In pregnancy it comes with the territory, because the kidneys filter harder. Only a diseased liver can really make production falter, and then the liver values beside it deviate as well. The lever sits in your glass and on your plate. With a high urea and a normal creatinine: drink regularly through the day, certainly around exercise and in warm weather, and check whether your protein intake is not higher than you need; for most athletes one and a half to two grams per kilo of body weight a day is plenty. With a low urea: check whether you get enough protein, especially if you eat plant-based or are older, because keeping muscle takes protein. Always read urea beside creatinine and eGFR. If those are normal, it is about fluid and food; if they deviate with it, it is about the kidneys, and then eGFR is the measure. Uric acid leaves the body by the same exit and often runs alongside.
What lowers it
Usually less coming in or more dilution, and rarely the liver.
| Cause | How often |
|---|---|
| Little protein in the dietUrea forms when protein is broken down, so less coming in means less production; in a lean plant-based pattern the ordinary outcome | Often |
| Drinking plentyWith plenty of fluid the kidneys take back less urea; urea is more sensitive to that than creatinine | Sometimes |
| Liver diseaseUrea is made in the liver; only with a seriously diseased liver does production falter, and then the liver values deviate too | Rare |
What raises it
More coming in, less fluid, or slower filtration.
| Cause | How often |
|---|---|
| DehydrationWith little fluid the kidneys take back water and urea together; urea then rises sooner than creatinine | Often |
| Plenty of protein in the dietMore protein breakdown yields more urea without the kidney changing; protein shakes and a protein-rich sports diet lift the value | Often |
| Reduced kidney functionThe kidney is the exit, so slower filtration lets the value climb; then creatinine and eGFR move with it | Often |
| Breakdown of your own tissueHeavy training, fever, prednisone and prolonged fasting make the body draw on muscle, and that nitrogen becomes urea | Sometimes |
| Bleeding in the stomach or gutBlood in the gut is digested as protein and raises urea, while creatinine stays normal | Rare |
How does an urea blood test work?
- Referral
- Not needed. You can have urea measured without going through your GP.
- Fasting
- Not needed. What you ate and drank in the days before does feed in; drink normally and skip a heavy training session the day before if you want a clean value.
- The draw
- One tube of blood from a vein in your arm, usually together with creatinine.
- The result
- A single number in mmol/L, usually available the same day. Compare it with your own lab's range, because that differs more here than for most values.
- Repeating
- With a high value and a normal creatinine: a week of normal drinking and eating, then again. If creatinine deviates with it, eGFR follows the course.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is urea?
Urea is the substance in which your body gets rid of the nitrogen from broken-down protein. Your liver makes it from ammonia, which is toxic, and your kidneys clear it. The value therefore moves with two things at once: how much protein you take in and how well your kidneys work. That makes urea less useful than creatinine for looking at your kidneys alone, and useful precisely for saying something about your food and drink.
What is a normal urea level?
That depends on your lab more than for most values. For an adult the upper limit sits between about 6.4 and 8.6 mmol/L; one lab lets it rise with age, to 14.2 over eighty, another uses one range for all adults. So compare your result with the range printed beside it, and read it beside your creatinine.
What does a raised urea mean?
It depends on what sits beside it. If your creatinine is normal, a raised urea almost always points at too little fluid or plenty of protein, or at breakdown of your own tissue from heavy training, fever or prednisone. If your creatinine deviates too, it is more about filtration itself, and then eGFR is the measure.
What does a low urea mean?
Usually little: little protein in the diet or drinking plenty, and in pregnancy it comes with the territory. Only a seriously diseased liver can make production falter, and then the liver values deviate too. Anyone who eats plant-based or is older can read a low urea as a question of whether enough protein comes in to keep muscle.
How do I lower my urea?
With a normal creatinine: drink regularly through the day, certainly around exercise and in warm weather, and check whether your protein intake is not higher than you need; for most athletes one and a half to two grams per kilo of body weight a day is plenty. A week of normal eating and drinking and then measuring again usually shows the difference.
Is a high urea from protein shakes bad for my kidneys?
Not with healthy kidneys. The number shows that more nitrogen is being cleared, and healthy kidneys can handle that. Anyone who already has reduced kidney function is advised to moderate protein, and then a rising urea is a signal. The difference sits in creatinine and eGFR, not in the urea itself.
Does a GP use urea to diagnose kidney damage?
No. Kidney damage is diagnosed on eGFR and on protein in the urine; urea is a supplement beside them. In advanced kidney disease it is followed closely, because it is then the substance that causes the symptoms.
Do I need to fast?
No. What you ate and drank in the days before does feed into the value, more than with creatinine, so drink normally and skip a heavy training session the day before if you want a clean value.
Which tests include urea?
Urea is part of Advanced, the broader panel. It is not orderable yet.
Related biomarkers
Sources
- 1.NHG guideline on chronic kidney disease (M109), Dutch College of General Practitioners. 2026. richtlijnen.nhg.org
- 2.Unilabs, Bepalingenklapper: ureum. 2026. bepalingenklapper.nl
- 3.Star-shl, Labbepalingen: ureum. 2026. star-shl.nl
- 4.Clinical Diagnostics, Labgids: ureum. 2026. clinicaldiagnostics.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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Urea is part of Advanced, the broader panel. It is not orderable yet.
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