Blood Urea Nitrogen

The BUN test should be interpreted with creatinine rather than alone for kidney function assessment. BUN is affected by protein intake, hydration status, and physiological stress, so it is not a pure kidney marker. The kidneys filter urea from circulation and excrete it in urine. Urea is transported in the bloodstream, filtered by the kidneys, and excreted in urine. The liver forms urea from nitrogen, carbon, and other elements, and urea enters the bloodstream. BUN levels are influenced by protein intake, hydration, metabolic rate, liver function, and kidney waste clearance. BUN reflects both urea production and renal elimination capacity. High protein diet consumption, steroid use, dehydration, burn injuries, and aging can elevate BUN levels. Kidney damage can cause urea to accumulate in blood and raise BUN. Elevated BUN can result from impaired liver protein breakdown or impaired kidney filtration of urea. Dietary protein breakdown produces ammonia as a nitrogenous byproduct. Blood urea nitrogen is produced when the liver metabolizes protein into urea.