Urea
A waste product from the breakdown of protein, cleared by the kidneys. Reported as urea (or as BUN in the US), it reflects kidney function, hydration and protein intake together — so it is always read with creatinine, which is more specific to the kidney.
What it measures
Urea is made in the liver when the body breaks down protein, and it is filtered out by the kidneys. Its blood level therefore depends on three things at once: how well the kidneys are working, how hydrated you are, and how much protein is entering the system. This makes urea a useful but non-specific marker. A raised urea can mean reduced kidney function, but very commonly it simply reflects dehydration (where it typically rises more than creatinine does), a high-protein intake, or blood in the gut being digested as protein (as in a gastrointestinal bleed). A low urea can reflect a low-protein diet, liver disease (where less urea is made), over-hydration, or pregnancy. Because of this, urea is always interpreted alongside creatinine and eGFR: the two together, and the ratio between them, help separate a true kidney problem from dehydration or other causes. (Urea is the same measurement reported as 'BUN' — blood urea nitrogen — in the United States.)
What a high value can mean
- Dehydration — a very common cause; urea rises more than creatinine (a high urea-to-creatinine ratio).
- Reduced kidney function — with a raised creatinine and low eGFR.
- Gastrointestinal bleeding — blood digested as protein raises urea.
- High-protein diet, tissue breakdown, some steroids.
- Heart failure — reduced kidney perfusion.
What a low value can mean
- Low-protein diet or malnutrition.
- Liver disease — the liver makes less urea.
- Over-hydration — dilutional.
- Pregnancy — a normal lower level.
When to discuss with a doctor
Urea is read together with creatinine and eGFR, not alone, because on its own it cannot separate a kidney problem from dehydration or diet. A raised urea with a normal creatinine most often points to dehydration and improves with fluids. A raised urea with a raised creatinine and a low eGFR points to reduced kidney function needing assessment. A disproportionately high urea can also be a clue to a gastrointestinal bleed when there are other signs. Mediora.AI shows urea alongside creatinine, eGFR and sodium so the pattern — kidney versus hydration — is visible, and reconciles the urea/BUN naming; the clinical interpretation belongs with your doctor.