There are prerenal, renal and postrenal causes of renal failure.
Disturbance of blood supply of kidneys is the main prerenal cause of renal failure (RF). It is assumed that the process of renal filtration (the first stage of uropoiesis) depends entirely on the amount of blood flowing to kidneys. This amount is determined by arterial pressure. Therefore, in most cases, acute renal failure (ARF) is caused by a sharp drop of arterial pressure, because it reduces significantly the amount of blood going to kidneys.
The cause of such a drop is a critical condition, a shock, which is characterized by a severe disorder of blood circulation. This shock condition is cause by a considerable loss of blood, traumas, burns (a hypovolemic shock), heart-work disorder (a cardiogenic shock in case of myocardial infarction), a septic shock (in case of sepsis), an anaphylactic shock (when getting specific allergens in the sensitized organism) and so forth.
Thus, during a critical drop of blood supply of kidneys the process of urine filtration becomes impossible and uropoiesis stops. This state is called anuria.