The bun is blood urea nitrogen. Creatinine is a natural waste that occurs at a low level in the body. Both BUN and creatinine are nitrogenous end products of metabolism, filtered by the kidney and excreted in the urine. Therefore Doctors measure the level of creatinine and BUN to check kidney and liver functions. High levels of creatinine and the BUN-creatinine ratio may indicate acute kidney injury or dehydration. Because of decreased muscle mass, elderly patients may have an elevated BUN:Cr at baseline Hypercatabolic states, high-dose glucocorticoids, and resorption of large hematomas have all been cited as causes of a disproportionate rise in BUN relative to the creatinine