Health & Medical intensive care

Comparison of Diagnostic Criteria of AKI in Critically Ill

Comparison of Diagnostic Criteria of AKI in Critically Ill

Abstract and Introduction


Introduction: Recently, the Kidney Disease: Improving Global Outcomes (KDIGO) proposed a new definition and classification of acute kidney injury (AKI) on the basis of the RIFLE (Risk, Injury, Failure, Loss of kidney function, and End-stage renal failure) and AKIN (Acute Kidney Injury Network) criteria, but comparisons of the three criteria in critically ill patients are rare.

Methods: We prospectively analyzed a clinical database of 3,107 adult patients who were consecutively admitted to one of 30 intensive care units of 28 tertiary hospitals in Beijing from 1 March to 31 August 2012. AKI was defined by the RIFLE, AKIN, and KDIGO criteria. Receiver operating curves were used to compare the predictive ability for mortality, and logistic regression analysis was used for the calculation of odds ratios and 95% confidence intervals.

Results: The rates of incidence of AKI using the RIFLE, AKIN, and KDIGO criteria were 46.9%, 38.4%, and 51%, respectively. KDIGO identified more patients than did RIFLE (51% versus 46.9%, P = 0.001) and AKIN (51% versus 38.4%, P <0.001). Compared with patients without AKI, in-hospital mortality was significantly higher for those diagnosed as AKI by using the RIFLE (27.8% versus 7%, P <0.001), AKIN (32.2% versus 7.1%, P <0.001), and KDIGO (27.4% versus 5.6%, P <0.001) criteria, respectively. There was no difference in AKI-related mortality between RIFLE and KDIGO (27.8% versus 27.4%, P = 0.815), but there was significant difference between AKIN and KDIGO (32.2% versus 27.4%, P = 0.006). The areas under the receiver operator characteristic curve for in-hospital mortality were 0.738 (P <0.001) for RIFLE, 0.746 (P <0.001) for AKIN, and 0.757 (P <0.001) for KDIGO. KDIGO was more predictive than RIFLE for in-hospital mortality (P <0.001), but there was no difference between KDIGO and AKIN (P = 0.12).

Conclusions: A higher incidence of AKI was diagnosed according to KDIGO criteria. Patients diagnosed as AKI had a significantly higher in-hospital mortality than non-AKI patients, no matter which criteria were used. Compared with the RIFLE criteria, KDIGO was more predictive for in-hospital mortality, but there was no significant difference between AKIN and KDIGO.


Acute kidney injury (AKI) is very common, especially in the intensive care unit (ICU). It is also associated with increased mortality and a longer stay in the hospital. There have been many definitions, such as acute renal failure and renal impairment, and this has made it difficult to compare results across studies. In 2004, the Acute Dialysis Quality Initiative group proposed a classification for AKI: the Risk, Injury, Failure, Loss of Kidney Function, and End-stage Kidney Disease (RIFLE) classification, the first evidence-based consensus. The classification includes three grades of severity of AKI (risk, injury, and failure) according to relative changes in serum creatinine (SCr) and urine output and two outcomes (loss of kidney function and end-stage kidney disease, or ESKD). It has been evaluated in many studies of critically ill patients with AKI and has shown good relevance for diagnosing and classifying the severity of AKI as well as comparable predictive ability for mortality.

In 2007, the Acute Kidney Injury Network (AKIN) group proposed a modified version of the RIFLE classification, which aimed to improve the sensitivity of AKI criteria. There were several changes: an absolute increase in SCr of at least 26.4 μmol/L was added to stage 1; patients starting RRT were classified as stage 3, irrespectively of SCr; and the change in glomerular filtration rate (GFR) and the two outcome classes were removed. AKI diagnosis was based on change between two creatinine values within a 48-hour period for AKIN classification and within a 1-week window for RIFLE criteria. Severity of AKI in AKIN is staged over the course of 7 days by fold-change in creatinine from baseline.

The latest classification was proposed by the Kidney Disease: Improving Global Outcomes (KDIGO) Acute Kidney Injury Work Group, was based on the previous two classifications, and had the aim of unifying the definition of AKI. According to this definition, AKI was diagnosed as an increase in SCr by at least 26.4 μmol/L within 48 hours or an increase in SCr to 1.5 times baseline, which is known or presumed to have occurred within 7 days before, or a urine volume of less than 0.5 mL/kg per hour for 6 hours. For KDIGO criteria, the 26.4 μmol/L increase needs to be within 48 hours but a 1.5-fold increase can occur within 7 days to diagnose AKI; and the 1-week or 48-hour timeframe is for diagnosis of AKI, not for staging. A patient can be staged over the entire episode of AKI. Increase in SCr to 3 times baseline, or SCr of more than 4.0 mg/dL (354 μmol/L), or starting RRT were all classified as stage 3. KDIGO removes the 0.5 mg/dL increase for creatinine more than 4 mg/dL to diagnose stage 3. Besides, KDIGO explicitly states that a rolling baseline can be used over 48-hour and 7-day periods for diagnosis of AKI, but it is unclear how this is handled in RIFLE or AKIN. The definition and difference among the three criteria are shown in Additional file 1

Many studies have compared RIFLE with AKIN in critically ill patients, but only a few have compared KDIGO with these criteria in critically ill patients with AKI. The purposes of this study were to determine the incidence of AKI in critically ill patients according to the RIFLE, AKIN, and KDIGO criteria and to compare their predictive ability.

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