Final answer:
Acute renal failure comprises three stages: Injury with a creatinine level 2 times normal or low urine output, Failure with a significant increase in creatinine or severely low urine output, and Loss indicating persistent kidney failure for more than four weeks.
Step-by-step explanation:
Acute renal failure (ARF), now more commonly referred to as acute kidney injury (AKI), is a serious condition that involves the rapid loss of kidney function. The stages of ARF can often be categorized based on the severity of the injury. According to recent classifications, the stages are as follows:
- Injury: This stage is characterized by a creatinine level that is 2 times the normal level or urine production that is less than 0.5 ml/kg for 12 hours.
- Failure: The failure stage of ARF presents with a threefold increase in creatinine from the baseline, creatinine level greater than 355 mmol/l with a rise of more than 44 mmol/l, or urine output below 0.3 ml/kg for 24 hours.
- Loss: This stage involves persistent ARF lasting for more than four weeks, indicating a complete loss of kidney function.
It is essential for ARF to be diagnosed and treated promptly to prevent permanent damage, and a kidney biopsy may be conducted in some cases to secure a definitive diagnosis unless the cause of ARF is quite clear and other investigative results are reassuringly negative.