Blood Urea Nitrogen (BUN) is a blood test that measures the amount of urea nitrogen in your blood. Urea is a waste product produced when the body breaks down protein. The BUN test helps assess how well your kidneys are functioning, as the kidneys filter urea from the blood and excrete it in urine. Elevated BUN levels can indicate kidney dysfunction, dehydration, or other health conditions. It's a key parameter in the Kidney Function Test (KFT).