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Chapter 73: Acute Kidney Injury

INTRODUCTION

  • Acute kidney injury (AKI) is a clinical syndrome generally defined by an abrupt reduction in kidney functions as evidenced by changes in serum creatinine (Scr), blood urea nitrogen (BUN), and urine output.

  • RIFLE (Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Renal Disease), AKIN (Acute Kidney Injury Network), and the Kidney Disease: Improving Global Outcomes (KDIGO) Clinical Practice Guidelines are three criteria-based classification systems developed to define and stage AKI in different patient populations (Table 73–1).

  • All three staging systems have been validated across different patient populations and their staging correlates closely with hospital mortality, cost, and length of stay.

  • Scr and urine output are the main diagnostic criteria for each staging system.

TABLE 73–1abcRIFLE, AKIN, and KDIGO Classification Schemes for Acute Kidney Injurya
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TABLE 73–1 RIFLE, AKIN, and KDIGO Classification Schemes for Acute Kidney Injurya
RIFLE Category Scr and GFRb Criteria Urine Output Criteria
Risk Scr increase to 1.5-fold or GFR decrease >25% from baseline <0.5 mL/kg/h for ≥6 hours
Injury Scr increase to twofold or GFR decrease >50% from baseline <0.5 mL/kg/h for ≥12 hours
Failure Scr increase to threefold or GFR decrease >75% from baseline, or Scr ≥4 mg/dL (≥354 μmol/L) with an acute increase of at least 0.5 mg/dL (44 μmol/L) Anuria for ≥12 hours
Loss Complete loss of function (RRT) for >4 weeks
ESKD RRT >3 months
AKIN Criteria Scr Criteria Urine Output Criteria
Stage 1 Scr increase ≥0.3 mg/dL (≥27 μmol/L) or 1.5- to 2-fold from baseline <0.5 mL/kg/h for ≥6 hours
Stage 2 Scr increase >2- to 3-fold from baseline <0.5 mL/kg/h for ≥12 hours
Stage 3 Scr increase >3-fold from baseline, or Scr ≥4 mg/dL (≥354 μmol/L) with an acute increase of at least 0.5 mg/dL (≥44 μmol/L), or need for RRT <0.3 mL/kg/h for ≥24 hours or anuria for ≥12 hours
KDIGO Criteria Scr Criteria Urine Output Criteria
Stage 1 Scr increase ≥0.3 mg/dL (≥27 μmol/L) or 1.5–1.9 times from baseline <0.5 mL/kg/h for 6–12 hours
Stage 2 Scr increase 2–2.9 times from baseline <0.5 mL/kg/h for ≥12 hours
Stage 3 Scr increase three times from baseline, or Scr ≥4 mg/dL (≥354 μmol/L), or need for RRT, or eGFRc <35 mL/min/1.73 m2 (<0.34 mL/s/m2) in patients <18 years Anuria for ≥12 hours

(AKIN, Acute Kidney Injury Network; ESKD, end-stage kidney disease; eGFR, estimated glomerular filtration rate; h, hours; KDIGO, Kidney Disease: Improving Global Outcomes; RIFLE, Risk, Injury, Failure, Loss of Kidney Function, and End-Stage Kidney Disease; RRT, renal replacement therapy; Scr, serum creatinine.)

a

For all staging systems, the criterion that leads to worst possible diagnosis should be used.

b

GFR calculated using the Modification of Diet in Renal Disease (MDRD) equation.

c

GFR calculated using ...

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