Acute renal failure is a condition when the kidneys suddenly fail to perform their normal functions, which includes the filtering of waste products and salt and fluid balance. There are three main categories why the kidney may show an acute deterioration in function which may lead to end stage renal disease requiring dialysis.  The first category is a drop of blood pressure to the kidneys secondary to bleeding, dehydration, or a severe infection in the body which causes sepsis and a drop in blood pressure.  The second main category which causes acute kidney disease are toxins, including certain medications such as antibiotics (gentamicin), certain antihypertensive medications such as the ACE inhibitors (enalapril, lisinopril), aspirin or ibuprofen in high doses, and the contrast dye used in various radiographic imaging studies.  The third main category of kidney failure is caused by a blockage of the passage of urine out of the kidneys and bladder secondary to a kidney stone, tumor, or an enlarged prostate gland.

Symptoms of acute renal failure should not be ignored and require immediate attention by the physician, specifcally a kidney specialist known as a nephrologist.  These symptoms include markedly diminished urine output, poor appetite and nausea, new swelling in the ankles and legs, mental confusion, and sometimes lower back or flank pain.
Thus, the patient starts passing less urine, and slowly the excretion of urine becomes so little, that on measuring it in 24 hours, it will be hardly 400 ml, while an individual is expected to pass about 1500-2000 ml of urine per day.

Laboratory studies including the serum creatinine and blood urea nitrogen (BUN) also become markedly elevated.  Serum creatinine is a more sensitive index of kidney function than blood urea, which varies with the intake of food by the patient.  The blood levels of BUN and creatinine rise dramatically if the kidney is not able to filter out the normal metabolic waste of the body, and if immediate medical treatment is not given to reverse the cause of the kidney failure.  The normal levels of serum creatinine are 0.8 mg/ dl to 1.4 mg/ dl, with an average 1.00 mg/ dl. If the levels of serum creatinine rise more than 8.00 mg/ dl, urgent dialysis is required to save the kidneys as well as the
life of the patient.