Acute Kidney Injury (AKI)
According to KDIGO, AKI is defined as an:
1) Increase in serum creatinine by ≥0.3 mg/dL within 48 hrs; OR,
2) Increase in serum creatinine to ≥1.5 times baseline (i.e. 50% above baseline), which is known or presumed to have occurred within the prior 7 days; OR,
3) Urine volume <0.5 mL/kg/h over a 6-hour period.
Acute kidney injury is most commonly diagnosed in hospitalized patients or following a procedure. AKI develops in hours to days.
Staging of AKI
KDIGO stages for AKI
| Stage | Serum Creatinine | Urine output |
| 1 | 1.5–1.9 times baseline (i.e. an increase of 50% to 99% from baseline) OR ≥0.3 mg/dl (≥26.5 μmol/l) increase |
<0.5 mL/kg/h for 6 to 12 hours |
| 2 | 2.0–2.9 times baseline | <0.5 mL/kg/h for 12 to 24 hours |
| 3 | 3.0 times baseline OR Increase in serum creatinine to ≥4.0 mg/dl (≥353.6 μmol/l) OR Initiation of renal replacement therapy OR, In patients <18 years, decrease in eGFR to <35 ml/min per 1.73 m2 |
<0.3 ml/kg/h for ≥24 hours OR Anuria for ≥12 hours |
Acute AKI vs. Subacute Kidney Injury vs. Chronic Kidney Disease
*** The distinction between acute kidney injury (AKI), subacute injury, and chronic kidney disease (CKD) is arbitrary. However, it is still helpful. See AKI definition above and subacute and CKD below.
Subacute Kidney Injury
Most patients with subacute kidney injury are evaluated as outpatients. By definition, subacute kidney injury develops more slowly than AKI but generally results in an increased creatinine in less than three months. In other words, subacute kidney injury evolves over more than 48 hours (the time frame for AKI) but in under three months (which is the time frame for CKD). Subacute Kidney injury occurs between AKI and CKD.
Chronic Kidney Disease (CKD)
CKD is defined by reduced GFR (ie, <60 ), an elevated creatinine, or other evidence of kidney damage, such as albuminuria or abnormal findings on renal imaging, that is relatively stable for 3 months or more and have implications for health.
Acute Kidney Diseases and Disorders (AKD)
AKD is a term used to describe any decrease in kidney function occurring in less than three months. It includes both AKI and Subacute kidney injury.
References
Source: https://kdigo.org/wp-content/uploads/2016/10/KDIGO-2012-AKI-Guideline-English.pdf Last accessed 5/17/2019