The renal failure index is the ratio of urinary sodium divided by urinary creatinine to blood creatinine, called the renal failure index, which is a very good indicator used to distinguish the cause of acute renal failure. Acute renal failure can be divided into pre-renal, renal and post-renal, all three of which can cause acute renal failure. Pre-renal factors generally refer to inadequate renal perfusion, such as dehydration, hemorrhagic shock, and heart failure, which cause pre-renal factors. Renal factors are often caused by tubular necrosis, interstitial lesions, renal vascular disease, and glomerular disease. A renal failure index greater than 1 often indicates acute renal failure due to renal factors. If the renal failure index is less than 1, it is often indicative of acute renal failure caused by prerenal factors.