BUN is the abbreviation of urea nitrogen and Cr is the abbreviation of creatinine, so BUN and Cr are both items in the kidney function test. BUN/Cr is to help determine the cause of acute kidney injury, whether it is pre-renal or renal renal failure. If the BUN/Cr exceeds 20, excluding the presence of gastrointestinal bleeding, it often indicates the presence of pre-renal factors leading to kidney injury, such as severe vomiting, diarrhea, blood and fluid loss or insufficient intake. If BUN/Cr is less than 10, renal failure is considered, and needs to be identified as a result of tubular necrosis, interstitial lesions, renal vascular disease, and glomerular disease. If it is between the 2, a prerenal factor is usually considered to be involved, and there may be a renal factor as well.