Acute kidney injury (AKI), formerly known as acute renal failure, refers to a sudden and often reversible decline in kidney function. This condition is typically characterized by a rapid increase in serum creatinine levels, a reduction in urine output, or both. The impairment of kidney function disrupts the kidneys' ability to filter blood effectively, leading to the accumulation of metabolic wastes, toxins, and fluids. While AKI can develop in a variety of clinical contexts, it is most prevalent in hospitalized patients, particularly those in intensive care units (ICUs). AKI is a serious condition with significant morbidity and mortality rates if left untreated, making prompt diagnosis and management critical.
The most widely accepted criteria for diagnosing AKI are the KDIGO (Kidney Disease: Improving Global Outcomes) guidelines. According to these criteria, AKI is defined by any of the following: an increase in serum creatinine by 0.3 mg/dL or more within 48 hours, an increase in serum creatinine to 1.5 times or more from the baseline within the prior 7 days, or a urine output of less than 0.5 mL/kg/h for 6 hours or more. Other diagnostic criteria, such as RIFLE (Risk, Injury, Failure, Loss, End-Stage Renal Disease) and AKIN (Acute Kidney Injury Network), are also used but have similar predictive capabilities in assessing in-hospital mortality.
| Criterion | Threshold |
|---|---|
| Absolute creatinine rise | Increase in serum creatinine of 0.3 mg/dL or more within 48 hours |
| Relative creatinine rise | Increase in serum creatinine to 1.5 times or more above baseline within the prior 7 days |
| Urine output | Less than 0.5 mL/kg/h for 6 hours or more |
