Urea (carbamide) is the product the liver converts ammonia into during protein breakdown. It is excreted by the kidneys, so its level reflects kidney function, protein metabolism and hydration.
Urea is a less accurate kidney marker than creatinine and GFR: it swings a lot with food and fluids. But together with creatinine it helps tell dehydration from kidney disease.
Reference ranges
Approximate reference for adults:
| Adults | 2.5 – 7.5 mmol/L |
| Elderly | the upper limit is slightly higher |
| Assess | together with creatinine and eGFR |
What an elevated level means
A rise in urea comes in three types:
"Pre-renal": dehydration, a heavy protein meal, GI bleeding, catabolism (tissue breakdown). The kidneys are healthy here.
Renal: reduced kidney function — then creatinine rises in parallel and eGFR falls.
"Post-renal": obstruction to urine flow.
An isolated rise in urea with a normal creatinine most often means dehydration or a lot of protein in the diet.
What a low level means
A low urea is usually not worrying. It is seen with a low-protein diet, in pregnancy (blood volume rises) and sometimes in severe liver disease, when the liver cannot keep up with urea synthesis.
How the test is done
Venous blood, fasting.
The day before, avoid overeating protein and heavy alcohol, and drink enough water. Always assess urea together with creatinine and eGFR, not on its own.
What affects the value
- Dietary protein — a lot of meat the day before raises urea.
- Hydration — dehydration raises it, excess water lowers it.
- Kidney function — reduced function raises the level.
- GI bleeding and catabolism — raise it.
- Liver function — severe liver disease lowers urea synthesis.
Calculate using this marker
Calculators where Urea is used directly:
Frequently asked questions
Urea is high — is it definitely the kidneys?
No. Urea depends heavily on food and fluids. An isolated rise with a normal creatinine most often means dehydration or a lot of protein in the diet. Kidneys are indicated by a simultaneous rise in creatinine and a fall in eGFR.
How does urea differ from creatinine?
Creatinine is produced from muscle at a steady rate and reflects filtration more accurately. Urea fluctuates with food and drink, but their ratio helps tell dehydration (a high ratio) from a genuine kidney problem.
How do I prepare for a urea test?
Test fasting, do not overeat protein or overindulge in alcohol the day before, and drink enough water. And assess the result together with creatinine and eGFR — using our GFR calculator.