Acute Kidney Injury and Kidney Replacement Therapy in the Critically Ill Patient
The primary difference between the RIFLE and the AKIN criteria is that AKIN includes a small
absolute change in SCr (0.3 mg/dL or more) as part of the diagnostic criteria for AKI and sets a 48-
hour time constraint for the criteria to be met. AKIN also omits the outcome classifications (loss and
end-stage) previously proposed in the RIFLE criteria.
In patients requiring KRT, AKIN stage 3 is met, regardless of the stage they are in when KRT is
initiated.
| d. | Several studies have validated these criteria and show that the more severe the RIFLE class or |
|---|
AKIN stage, the worse the clinical outcome.
In 2012, a third consensus definition was introduced, the Kidney Disease: Improving Global Outcomes
(KDIGO) classification system, which is the current criterion standard.
Separately, the RIFLE criteria and the AKIN criteria were each shown to be suboptimally sensitive
for detecting AKI.
The KDIGO criteria combine the strengths of both RIFLE and AKIN, retain the AKIN criteria of a
rise in SCr of 0.3 mg/dL within 48 hours, and allow 7 days for a 50% increase in SCr from baseline,
as seen in RIFLE.
Despite these updates, limitations exist with current definitions.
Current diagnostic markers (SCr and urine output) reflect loss of function rather than damage or
injury.
SCr is an imperfect biomarker for estimation of glomerular filtration rate and is significantly affected
by muscle mass. In the critically ill, production may be decreased and volume of distribution may be
affected by volume overload, both decreasing SCr levels.
Baseline SCr values may not be available in all patients. Various techniques may be used such as
admission SCr, inpatient nadir SCr, imputed creatinine using estimated glomerular filtration rate
(eGFR) 75 mL/min/1.73m2, or preadmission baseline, all with certain strengths and limitations.
| d. | Decreased urine output is a physiologic response to intravascular volume depletion and may not |
|---|
imply tubule injury. It is also confounded by use of diuretics.
Current consensus definitions do not address the subphenotypes of AKI, which may support future
development of therapeutics or trial enrichment for management of AKI.
RIFLE
AKIN
KDIGO
All Three
Classification
Systems
Stage
SCr/GFR Criteria
Stage
SCr Criteria
Stage
SCr Criteria
UOP Criteria
R
Increase to ≥ 1.5-fold
or GFR decrease
> 25% from baseline
Increase to 1.5- to
2-fold above baseline
or by ≥ 0.3 mg/dL
within 48 hr
Increase to 1.5- to
< 2-fold above base-
line over 7 days or by
≥ 0.3 mg/dL within
48 hr
< 0.5 mL/kg/hr
for 6-12 hr
I
Increase to ≥ 2-fold
or GFR decrease
> 50% from baseline
Increase to ≥ 2- to
3-fold above baseline
Increase to ≥ 2- to
< 3-fold above
baseline
< 0.5 mL/kg/hr
for ≥ 12 hr
F
Increase to ≥ 3-fold,
GFR decrease > 75%
from baseline, or SCr
≥ 4 mg/dL (acute
increase of at least
0.5 mg/dL)
Increase > 3-fold
above baseline or ≥ 4
mg/dL with an acute
rise of ≥ 0.5 mg/dL or
on KRT
Increase ≥ 3-fold
above baseline or ≥ 4
mg/dL or initiation of
KRT
< 0.3 mL/kg/
hr for ≥ 24 hr
or anuria for ≥
12 hr