Biomarker . Patient guide
Urea Blood Test
What is Urea
Urea is a waste product made by the liver when protein is broken down, and it is cleared by the kidneys. Measured alongside creatinine and electrolytes (a U&E), it gives a picture of kidney function and hydration.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in mmol/L. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Adults | 2.5 to 7.8 | mmol/L; varies between labs |
What it is
Protein metabolism produces ammonia, which the liver converts to urea for safe excretion by the kidneys. Blood urea therefore reflects the balance of protein breakdown, hydration, and kidney clearance, which is why it is interpreted together with creatinine rather than alone.
Why a clinician would order it
Urea is checked to assess kidney function, hydration and, in some settings, gastrointestinal bleeding (which raises urea disproportionately). It is a standard part of a U&E and a general health screen.
If your level is outside the range
Symptoms of low Urea
What low can indicate. Low protein intake, liver disease (reduced urea production), overhydration, or pregnancy.
Symptoms of high Urea
- Often none when mildly raised
- With significant kidney impairment: tiredness, poor appetite, nausea
What high can indicate. Dehydration (the commonest cause of a mild rise), reduced kidney function, a high-protein diet, or an upper gastrointestinal bleed. A urea raised out of proportion to creatinine usually points to dehydration or GI bleeding rather than intrinsic kidney disease.
Testing tips
No fasting needed. Hydration status strongly affects the result, so a raised urea with a normal creatinine is often simply dehydration and worth repeating after rehydrating.
Related markers
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about Urea
What is a normal Urea range?
Adults: 2.5 to 7.8 (mmol/L; varies between labs). Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low Urea result mean?
Low protein intake, liver disease (reduced urea production), overhydration, or pregnancy.
What does a high Urea result mean?
Dehydration (the commonest cause of a mild rise), reduced kidney function, a high-protein diet, or an upper gastrointestinal bleed. A urea raised out of proportion to creatinine usually points to dehydration or GI bleeding rather than intrinsic kidney disease.
Do I need to fast or prepare for the Urea blood test?
No fasting needed. Hydration status strongly affects the result, so a raised urea with a normal creatinine is often simply dehydration and worth repeating after rehydrating.
Can I order a Urea blood test privately in London?
Yes. WMG Health offers Urea as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.