Urea
Urea (blood urea nitrogen, BUN) is a waste product from protein metabolism. The liver converts ammonia (from amino acid deamination) into urea, which is filtered by the kidneys. Unlike creatinine, urea is partially reabsorbed by the kidneys (40-60%), making it more variable and less specific for kidney function.
Why it matters: Urea is useful in combination with creatinine. The urea/creatinine ratio helps distinguish pre-renal azotemia (dehydration, heart failure — high ratio) from intrinsic kidney disease (normal ratio). Elevated urea with normal creatinine may indicate high protein intake, GI bleeding (digested blood = protein load), or dehydration.
May increase with:
May decrease with:
What is Urea?
Urea (blood urea nitrogen, BUN) is a waste product from protein metabolism. The liver converts ammonia (from amino acid deamination) into urea, which is filtered by the kidneys. Unlike creatinine, urea is partially reabsorbed by the kidneys (40-60%), making it more variable and less specific for kidney function.
What might a high or low Urea mean?
Urea is useful in combination with creatinine. The urea/creatinine ratio helps distinguish pre-renal azotemia (dehydration, heart failure — high ratio) from intrinsic kidney disease (normal ratio). Elevated urea with normal creatinine may indicate high protein intake, GI bleeding (digested blood = protein load), or dehydration.
What is the typical reference range for Urea?
The general-population reference range shown here is 2.5 – 6.4 mmol/L. Reference ranges describe the general population and are not a personal target — discuss your results with your physician.
What can affect Urea?
It may be higher with: Kidney disease (reduced excretion), Dehydration and volume depletion, High protein diet, GI bleeding (digested blood acts as protein load), Heart failure (reduced kidney perfusion), Catabolic states (burns, fever, surgery), Corticosteroids, Tetracycline antibiotics. It may be lower with: Low protein diet, Liver disease (reduced urea synthesis), Pregnancy (increased kidney filtration), Overhydration (dilution), SIADH.