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Essentials of Diagnosis

  • Acute increase in blood urea nitrogen (BUN) and serum creatinine.

  • May be associated with oliguria or normal urine output.

  • Symptoms and signs depend on etiology and comorbidities.


Acute kidney injury (AKI) is a life-threatening disease process occurring in approximately 5% of all hospitalized patients and up to 30% admissions to intensive care units. AKI is preferred to acute renal failure as both kidney and injury are more patient appropriate terms. Patients with AKI, regardless of their associated comorbid conditions, have greater than fivefold increased mortality rate. The hallmark for AKI is a reduction in the glomerular filtration rate (GFR), resulting in retention of nitrogenous wastes (creatinine, blood urea nitrogen [BUN], and other molecules that are not routinely measured). Early in the course of AKI patients are often asymptomatic and the condition is only diagnosed by observed elevations of BUN and serum creatinine levels or oliguria.

In 2002, the Acute Dialysis Quality Improvement Initiative (ADQI) proposed the first consensus definition scheme (RIFLE) of AKI. Since then, the Acute Kidney Injury Network (AKIN Criteria) proposed a modification of the RIFLE classification that includes the Risk, Injury, and Failure criteria with the addition of a greater than or equal to 0.3 mg/dL increase in the serum creatinine to the criteria that define risk (Table 9–1). Finally, KDIGO has modified these classification schemes.

Table 9–1.KDIGO criteria for AKI.

Oliguria (urine output <400 mL/24 hours or 15 mL/h in adults) occurs commonly in AKI and may be an important indicator of renal dysfunction. However, urine output cannot be solely used as a measure of kidney function. Patients with nonoliguric AKI usually have a better prognosis primarily due to less severe injury and or a higher incidence of nephrotoxic-induced AKI in the nonoliguric group. Unfortunately, there has been little improvement in survival from AKI since the advent of hemodialysis (HD), and the mortality remains greater than 50% in many studies.


Bellomo  R  et al: Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care 2004;8:R204.  [PubMed: 15312219]
KDIGO Clinical Practice Guideline for Acute Kidney Injury. Kidney Int Suppl 2012;2:1.

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