Urea
What it measures, and what changes the number.
Urea is a waste product formed in the liver when the body breaks down protein. It travels in the blood to the kidneys, which filter it out into the urine. The test measures the concentration of urea in the blood.
It is usually read alongside creatinine and eGFR as part of a kidney or basic metabolic panel, often with sodium and potassium. Some labs report urea itself, while others report BUN (urea nitrogen), which measures only the nitrogen part of the urea molecule, so the two figures are on different scales.
The result is influenced by hydration, recent protein intake, and bleeding in the gut, as well as by kidney function. Labs using different units or reporting BUN instead of urea will show numbers that are not directly comparable.
Often read alongside: Creatinine, BUN (urea nitrogen), eGFR (CKD-EPI), Sodium, Potassium