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Definition of Acute Kidney Injury

Acute kidney injury (AKI) is a condition defined by an acute decrease in the glomerular filtration rate (GFR), resulting in dysregulation of volume, electrolytes, acid-base balance and inability to excrete metabolic waste products. The term AKI has replaced the older term acute renal failure (ARF) to highlight the varying degrees of renal dysfunction, to enable clinicians to recognize renal dysfunction earlier in the patient’s course, and to allow researchers to apply a uniform definition of acute renal dysfunction.1 The Acute Dialysis Quality Initiative (ADQI) and Acute Kidney Injury Network (AKIN) groups standardized the definition of AKI in adult patients based on the increase in serum creatinine (Cr) or oligoanuria, and the pediatric community has adopted modified criteria based on the ADQI and AKIN definitions (Table 42-1).2

Table 42-1Acute Kidney Injury Definitions Using RIFLE, pRIFLE, and AKIN

Definition of AKI in Neonates and Infants

There are additional important factors to consider in defining AKI in neonates using serum Cr and urine output criteria. First, neonatal serum Cr following birth reflects maternal Cr, and it decreases to a steady state over 1 to 2 weeks in term infants and over 3 to 4 weeks in preterm infants as the neonate’s GFR steadily improves.3, 4 Tables 42-2 and 42-3 show the increasing GFR in preterm and term neonates.5, 6 Second, unlike in critically ill adults or children, critically ill neonates may not have their serum Cr measured daily due to the concern for blood loss, and AKI may go unrecognized.7 Elevated bilirubin levels can interfere with the Jaffe reaction assay, a common laboratory method used to measure serum Cr, and lead to an underestimation in the serum Cr if the laboratory does not correct for the ...

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