Urea

Urea is a waste product formed when the liver metabolizes proteins and is normally filtered by the kidneys and excreted in urine. Clinically measured as blood urea nitrogen (BUN), it helps assess kidney and liver function. While BUN is commonly used alongside creatinine to evaluate renal clearance, it is influenced by non-renal factors such as protein intake, hydration status, gastrointestinal bleeding, and catabolic states where tissues are being broken down. This makes BUN a useful but non-specific marker, best interpreted in the context of other clinical findings.[63]

[63]Levey P discussant: AS. Measurement of renal function in chronic renal disease. Kidney Int. 1990;38(1):167-184. doi:10.1038/ki.1990.182