Brief Answer: the kidneys are failing to do their job Detailed Answer: HI, thanks for using healthcare magic Renal ( refers to the kidneys) failure means that the kidneys are not working as they should. Renal failure can be acute or chronic. (1) Acute renal failure is short term kidney failure. In acute renal failure the damage to the kidneys occurs suddenly or abruptly. There are different causes such as dehydration, heart failure, blood clot, obstruction of urine flow, infection. Usually when the problem is treated the kidney starts to work as it did before. (2)Chronic renal failure is long term kidney failure- the changes have occurred over a long period of time. There are different stages, it may be mild or more serious. It can result from high blood pressure, diabetes, age related decrease in kidney function, cysts of the kidneys, inflammatory disease of the kidneys I hope this helps, feel free to ask any other questions

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