Risk (R)Mortality ~8.8%Creatinine ×1.5 above baseline OR GFR decrease >25%<0.5 mL/kg/hr for >6 hours
Injury (I)Mortality ~11.4%Creatinine ×2.0 above baseline OR GFR decrease >50%<0.5 mL/kg/hr for >12 hours
Failure (F)Mortality ~26.3%Creatinine ×3.0 OR Cr ≥4 mg/dL (acute rise ≥0.5) OR GFR decrease >75%<0.3 mL/kg/hr for >24h OR Anuria for >12h
Loss + End-StageRRT dependentComplete loss >4 weeks (L) / >3 months (E)RRT dependent
Worst-of Rule: Final RIFLE stage = the more severe of either the Creatinine/GFR criterion OR the Urine Output criterion. If creatinine = Risk but UO = Failure, the RIFLE stage = Failure.
Select Clinical Criteria
Cr
Creatinine / GFR Criteria
Select the creatinine change from baseline or GFR decrease. Use baseline creatinine prior to acute illness onset.
—
UO
Urine Output Criteria
Select urine output status. Measure in mL/kg/hr based on actual body weight. Oliguria must be sustained for the stated duration.
—
Cr/GFR StageBaseline
→ worst of →
UO StageNormal
=
RIFLE StageNo AKI
RIFLE AKI Stage—
—
—
No AKI
Risk (R)
Injury (I)
Failure (F)
Creatinine/GFR Stage—
vs
Urine Output Stage—
Worst-of = —
Recommended Clinical Action
—
AKIN Equivalent Stage
—
⚠️ RRT Consideration — AEIOU Indications
Assess for absolute RRT indications. Any single indication below warrants urgent nephrology consultation and RRT initiation discussion:
A
AcidosisSevere metabolic acidosis pH <7.1 refractory to bicarbonate therapy — often from uremic acid accumulation or lactic acidosis in RIFLE Failure
E
ElectrolytesHyperkalemia K⁺ >6.5 mEq/L or rapidly rising despite calcium gluconate, insulin/dextrose, and kayexalate — risk of fatal arrhythmia
I
IntoxicationDialyzable toxins: methanol, ethylene glycol, lithium, salicylates, theophylline — remove before irreversible organ damage
O
OverloadFluid overload with pulmonary edema, respiratory failure, or abdominal compartment syndrome refractory to high-dose diuretics
U
UremiaUremic encephalopathy, uremic pericarditis, uremic bleeding (platelet dysfunction) — typically BUN >80–100 mg/dL with symptoms
Clinical Interpretation
AKI / Renal Assessment Note
RIFLE Criteria — Complete Reference Table
RIFLE Stage
Creatinine / GFR Criterion
Urine Output Criterion
Approx. Mortality
Clinical Action
Risk (R)
Creatinine ×1.5 above baseline OR GFR decrease >25%
Sustained RRT; assess for renal recovery potential; nephrology + ethics if chronic dependence expected
End-Stage (E)
Irreversible end-stage kidney disease — ESRD
RRT dependent for >3 months
Very High
Chronic renal replacement therapy; transplant evaluation; palliative care discussion if appropriate
Mortality data: Bagshaw SM et al. Crit Care. 2008. RIFLE Failure stage carries the highest mortality (26.3%) — each stage independently increases in-hospital mortality risk.
RIFLE vs AKIN — Staging Comparison
AKIN Stage
RIFLE Equivalent
AKIN Creatinine Criterion
AKIN UO Criterion
Key Difference
Stage 1
Risk (R)
Cr ×1.5 OR absolute rise ≥0.3 mg/dL within 48h
<0.5 mL/kg/hr for >6h
AKIN adds 0.3 mg/dL absolute rise — more sensitive for early AKI
Stage 2
Injury (I)
Cr ×2.0 from baseline
<0.5 mL/kg/hr for >12h
Equivalent to RIFLE Injury
Stage 3
Failure (F)
Cr ×3.0 OR Cr ≥4.0 mg/dL (acute rise) OR RRT initiated
<0.3 mL/kg/hr for >24h OR Anuria >12h
AKIN Stage 3 adds: any patient requiring RRT
KDIGO 2012 unified both systems: AKI = absolute Cr rise ≥0.3 mg/dL in 48h OR Cr ×1.5 within 7 days OR UO <0.5 mL/kg/hr for ≥6h. KDIGO stage 1/2/3 corresponds approximately to AKIN Stage 1/2/3 and RIFLE R/I/F.
RIFLE Criteria — Clinical Reference for AKI Staging
The RIFLE criteria were developed by the Acute Dialysis Quality Initiative (ADQI) working group (Bellomo et al. 2004) to standardize the definition and severity classification of Acute Kidney Injury (AKI).
Before RIFLE, AKI had over 35 different definitions in the literature, making comparisons between studies impossible.
RIFLE unified the field using two measurable criteria — serum creatinine change from baseline and urine output — with a worst-of staging rule.
The "Worst-Of" Staging Rule — Critical for Correct Classification
The final RIFLE stage is always the more severe of either the creatinine/GFR criterion or the urine output criterion for any given patient.
If a patient has creatinine ×1.5 (Risk) but urine output of 0.2 mL/kg/hr for 26 hours (Failure), the RIFLE stage is Failure — not Risk.
This worst-of rule prevents underestimation of AKI severity when one marker lags behind the other, as commonly occurs in early oliguric AKI before creatinine has risen, or in non-oliguric AKI where creatinine rises despite preserved urine output.
RIFLE vs AKIN vs KDIGO — Which to Use?
All three systems broadly correlate and identify the same patients.
RIFLE is most commonly referenced in older literature (pre-2012) and remains widely used for epidemiological and research purposes.
AKIN added the 0.3 mg/dL absolute creatinine rise criterion (within 48 hours) — more sensitive for detecting early AKI in patients with already-elevated creatinine.
KDIGO 2012 unified both: AKI = creatinine rise ≥0.3 mg/dL in 48 hours, OR ×1.5 within 7 days, OR urine output <0.5 mL/kg/hr for ≥6 hours. KDIGO stages 1/2/3 correspond to AKIN 1/2/3 and RIFLE R/I/F. Most current guidelines use KDIGO 2012.
RRT Indications — AEIOU Mnemonic
A — Acidosis: Severe metabolic acidosis pH <7.1 refractory to bicarbonate therapy — often from uremic acid accumulation or lactic acidosis in RIFLE Failure
E — Electrolytes: Hyperkalemia K⁺ >6.5 mEq/L or rapidly rising despite calcium gluconate, insulin/dextrose, and kayexalate — risk of fatal arrhythmia
I — Intoxication: Dialyzable toxins: methanol, ethylene glycol, lithium, salicylates, theophylline — remove before irreversible organ damage
O — Overload: Fluid overload with pulmonary edema, respiratory failure, or abdominal compartment syndrome refractory to high-dose diuretics
U — Uremia: Uremic encephalopathy, uremic pericarditis, uremic bleeding (platelet dysfunction) — typically BUN >80–100 mg/dL with symptoms
What is the baseline creatinine in RIFLE if I don't know it?
When the baseline creatinine is unknown, KDIGO and AKIN guidelines recommend back-calculating a "presumed baseline" using the MDRD equation targeting a GFR of 75 mL/min/1.73m² for the patient's age, sex, and race. For example: in a 65-year-old African-American male, the back-calculated baseline creatinine = approximately 1.2 mg/dL. This approach has limitations — it assumes normal pre-illness renal function and will overestimate AKI severity in patients with chronic kidney disease. Always document whether baseline creatinine was measured or estimated.
What is non-oliguric AKI and how is it staged by RIFLE?
Non-oliguric AKI occurs when creatinine rises significantly despite urine output remaining above 0.5 mL/kg/hr — the kidney is injured but still producing urine. This is common in nephrotoxic AKI (aminoglycosides, contrast nephropathy, NSAIDs) and some forms of intrinsic renal disease. In RIFLE, non-oliguric AKI is staged solely by the creatinine criterion (since UO criterion is not met). Non-oliguric AKI generally carries better prognosis than oliguric AKI at the same creatinine stage, but still requires nephrology input and removal of nephrotoxins.
What are the causes of AKI that RIFLE staging does not distinguish?
RIFLE stages severity but does not identify cause. AKI causes are classified as: Pre-renal (hypovolemia, low cardiac output, hepatorenal syndrome — typically responds to fluid resuscitation; FENa <1%, FeUrea <35%); Intrinsic renal (acute tubular necrosis from ischemia or nephrotoxins, acute interstitial nephritis, glomerulonephritis — FENa >2%, muddy brown casts on urinalysis); Post-renal/obstructive (bladder outlet obstruction, bilateral ureteric obstruction — renal ultrasound shows hydronephrosis, often rapidly reversible). Distinguishing cause is essential as treatment differs completely — fluid for pre-renal, remove offending agents for intrinsic, relieve obstruction for post-renal.
When is CRRT used instead of intermittent hemodialysis in AKI?
Continuous Renal Replacement Therapy (CRRT) is preferred over intermittent hemodialysis (IHD) in hemodynamically unstable patients who cannot tolerate the rapid fluid and solute shifts of IHD. Typical CRRT indications in RIFLE Failure/AKIN Stage 3: hemodynamic instability requiring vasopressors; cerebral edema (liver failure, TBI); severe fluid overload in hypotensive patients; need for very precise fluid balance control. IHD is preferred when: patient is hemodynamically stable; early mobilization/rehabilitation is planned; anticoagulation is contraindicated (CRRT requires more anticoagulation); resource limitations. The KDIGO 2012 guidelines state that either modality is acceptable for hemodynamically stable patients with AKI requiring RRT.