Acute renal failure (ARF) is a sudden decrease in kidney function that results in the buildup of waste products in the blood. It can be caused by decreased blood flow to the kidneys, direct kidney damage, or urinary tract obstruction. The most common type is prerenal ARF due to low blood volume or pressure. Symptoms include thirst, dizziness, and reduced urine output. Treatment focuses on correcting the underlying cause, managing fluid balance and dialysis if needed. ARF is usually reversible but can last weeks depending on the severity of the initial insult.