The annual incidence is about 150 per million in the UK, but this figure is six times greater in the >80 years old group. Prerenal azotemia is considered as the most serious reason in community or hospital acquired acute renal failure (ARF). A 67-year-old middle age male was admitted to the hospital with a chief complaint of generalized weakness, volume depletion and dysuria. He has treated with metronidazole for diarrhoea caused by Clostridium difficile considered as the precipitating factor for the ARF. The patient has severe osteoarthritis and takes high dose non-steroidal anti-inflammatory drugs from the last two years. He also complains for obstructive sleep apnea (OSA) and obesity. He has controlled hypertension was on lisinopril to control blood pressure. ARF is quite common, occurring in 80 million populations. Urinary obstruction should be excluded (a cause in around 5-10 of cases) because this is readily reversible if it is diagnosed early. A renal US will be sufficient to identify obstruction in 95 of cases. Most cases of ARF are expected to pre renal failure/acute tubular necrosis (ATN) 70-80%. Risk factor for development for at ATN are old age, drugs (non-steroidal anti-inflammatory drugs, gentamicin), sepsis, and chronic kidney disease and must be considered.