Acute renal failure classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]; Serge Korjian; Yazan Daaboul; Rim Halaby

Overview

Acute renal failure can complicate a wide spectrum of disorders, and for the purpose of diagnosis and management is divided according to the mechanism that lead to renal compromise. The three categories are pre-renal azotemia (diseases that cause renal hypoperfusion), renal azotemia (diseases directly affecting the renal parenchyma), and post-renal azotemia (diseases affecting the urinary tract causing obstruction). However, the first consensus definition described and the most used definition is known as the RIFLE criteria. The acronym combines a classification of 3 levels of renal dysfunction (Risk, Injury, Failure) with 2 clinical outcomes (Loss, ESRD) to give the RIFLE stages of AKI.

Classification

The Levels of Renal Dysfunction

Acute renal failure is usually categorized (as in the flowchart below) according to pre-renal, renal and post-renal causes.

Acute Renal Failure

Pre-renal

Renal

Post-renal

1. Pre-renal

• Compromise in the renal blood flow

2. Renal

• Damage to the kidney itself

3. Post-renal

• Obstructive causes in the urinary tract

RIFLE Criteria

The RIFLE (Risk of renal dysfunction, Injury to the kidney, Failure or Loss of kidney function, and End-stage kidney disease) criteria classifies acute renal failure according to the probable clinical outcomes. The acronym combines a classification of 3 levels of renal dysfunction (Risk, Injury, Failure) with 2 clinical outcomes (Loss, ESRD). This unified classification was proposed to enable a viable comparison in trials of prevention and therapy and to observe clinical outcomes of the defined stages of AKI.

Proposed classification scheme for acute kidney injury (RIFLE) according to the Acute Dialysis Quality Initiative.

CLASSIFICATION	GFR CRITERIA	URINE OUTPUT CRITERIA
Risk	1.5x increase in SCr or GFR decrease >25%	<0.5 mL/kg/h for 6 hours
Injury	2x increase in SCr or GFR decrease >50%	<0.5 mL/kg/h for 12 hours
Failure	3x increase in SCr or GFR decrease >75%	<0.3 mL/kg/h for 24 hours or anuria for 12 hours
Loss	Complete loss of renal function >4 weeks
End Stage Renal Disease	Complete loss of renal function >3 months

Modified RIFLE Criteria

In 2007, the Acute Kidney Injury Network (AKIN) proposed modified diagnostic criteria based on the RIFLE criteria. AKI was defined as an acute increase in the serum creatinine of ≥ 0.3 mg/dL from baseline within 48 hours, a 50% increase in the serum creatinine concentration, or oliguria <0.5 mL/kg/h for 6 hours (following volume status optimization). The staging criteria retained the Risk, Injury, & Failure stages from the RIFLE criteria, with modifications related to serum creatinine increase.

Modified RIFLE classification scheme for acute kidney injury according to the Acute Kidney Injury Network (AKIN)

CLASSIFICATION	SERUM CREATININE CRITERIA	URINE OUTPUT CRITERIA
Stage 1	Increase in SCr ≥0.3 mg/dL or 1.5x to 2x increase from baseline	<0.5 mL/kg/h for 6 hours
Stage 2	2x to 3x increase in SCr from baseline	<0.5 mL/kg/h for 12 hours
Stage 3	>3x increase in SCr or SCr≥ 4.0 mg/dL with acute increase >0.5 mg/dL	<0.3 mL/kg/h for 24 hours or anuria for 12 hours

In March 2012, the Kidney Disease – Improving Global Outcomes (KDIGO) Clinical Practice Guidelines for Acute Kidney Injury retained the AKIN staging criteria while implementing modifications to the definition of AKI. AKI was defined as either an increase in serum creatinine by 50% in 7 days, an increase in serum creatinine by 0.3 mg/dL in 2 days, or anuria for more than 12 hours.