Urea
Blood Urea Nitrogen
What this test measures
Urea is a waste product made when your body breaks down protein. Healthy kidneys remove urea from your blood. This test helps check how well your kidneys are working.
Understanding the numbers
Typical range: 2.5-7.8 mmol/L
Urea can be affected by diet (high protein intake) and hydration, not just kidney function.
- Low: 1–2.5 mmol/L
- Normal: 2.5–7.8 mmol/L
- Mildly raised: 7.8–15 mmol/L
- Markedly raised: 15–40 mmol/L
Key numbers
- 7.8 mmol/L — Upper limit of normal
- 20 mmol/L — Marked rise — kidney failure or severe dehydration
- 10 mmol/L — Urea rising disproportionately to creatinine — think GI bleed or dehydration
Typical UK range. Urea is less kidney-specific than creatinine — it also rises with dehydration, high-protein diet, GI bleeding, and steroid use. A urea:creatinine ratio above 100:1 often indicates pre-renal cause (dehydration) or upper GI bleed.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Your kidneys may not be removing waste as well as they should
- Can also be raised by dehydration
- High protein diet can raise urea
- Bleeding in the gut can also cause raised levels
Questions you could ask your GP
- Is this result related to my kidney function?
- Should I drink more water?
- Do I need to change my diet?
- How often should my kidney function be checked?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Dehydration — high urea, creatinine stable
Albert had flu and poor fluid intake for a week. Urea 14.2, creatinine 105 (baseline 95). Urea:creatinine ratio very high.
What the GP said: “This pattern — high urea with only a small rise in creatinine — suggests you're dehydrated rather than having kidney disease. Small sips often, and we'll recheck in 48 hours.”
What happened next: With better hydration, urea was 6.5 at 48 hours.
Urea rises out of proportion to creatinine in dehydration and gastrointestinal bleeding. The urea:creatinine ratio gives a clue — often more useful than the numbers alone.
GI bleed — raised urea from absorbed blood
Bindu had black tarry stools, lightheadedness, and a haemoglobin of 88. Urea 18, creatinine 92.
What the GP said: “A raised urea with a normal-ish creatinine, plus black stools, points strongly to an upper GI bleed. I'm admitting you now for endoscopy.”
What happened next: Endoscopy found a duodenal ulcer; it was treated and PPI started.
An upper GI bleed increases urea because blood protein is digested and absorbed. Disproportionately high urea + melaena = upper GI bleed until proven otherwise.
Severe kidney failure — urea and creatinine both high
Frank presented with drowsiness and poor urine output. Urea 32, creatinine 420, K 6.1.
What the GP said: “Your kidneys have failed. This needs urgent hospital assessment — you may need dialysis.”
What happened next: Frank was admitted; he had acute-on-chronic kidney failure, needed short-term dialysis, and recovered most of his baseline function.
When both urea and creatinine are markedly raised, kidney failure is likely. Alongside symptoms (drowsiness, low urine output, breathlessness) it's a hospital emergency.
Low urea — pregnancy
Lily was 22 weeks pregnant. Urea 1.8 — below the standard range. She felt well and her creatinine was normal.
What the GP said: “Pregnancy increases blood volume and your kidneys work a bit harder, so urea drifts lower. This is normal — we don't need to do anything.”
Low urea is rarely a problem. Pregnancy and liver disease are the most common reasons. Without symptoms, no action is needed.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.