What indicates Acute Kidney Injury (AKI) in patients with Chronic Kidney Disease (CKD)?

Indicators of Acute Kidney Injury (AKI) on Chronic Kidney Disease (CKD)

An acute kidney injury superimposed on chronic kidney disease is indicated by an abrupt increase in serum creatinine by ≥0.3 mg/dL within 48 hours or an increase to ≥1.5 times baseline within 7 days, or urine output <0.5 mL/kg/h for 6 hours, in a patient with pre-existing kidney disease. 1

Diagnostic Criteria for AKI on CKD

Serum Creatinine Criteria

• Increase in serum creatinine by ≥0.3 mg/dL (26.5 μmol/L) within 48 hours, OR
• Increase in serum creatinine to ≥1.5 times baseline, which is known or presumed to have occurred within the prior 7 days 1

Urine Output Criteria

• Urine output <0.5 mL/kg/h for 6 hours 1

AKI Staging in CKD Patients

Stage	Serum Creatinine	Urine Output
1	1.5-1.9 times baseline OR ≥0.3 mg/dL increase	<0.5 mL/kg/h for 6-12h
2	2.0-2.9 times baseline	<0.5 mL/kg/h for ≥12h
3	3.0 times baseline OR increase to ≥4.0 mg/dL OR initiation of RRT	<0.3 mL/kg/h for ≥24h OR anuria for ≥12h

Special Considerations for AKI on CKD

Different Manifestation Patterns

• CKD patients may fulfill different KDIGO criteria compared to those with normal baseline kidney function:
  • CKD patients more frequently reach the absolute creatinine threshold (≥4.0 mg/dL) 2
  • Patients with normal baseline kidney function more commonly meet the relative increase criterion (≥3.0× baseline) 2

Diagnostic Challenges

• The percentage increase in serum creatinine can delay AKI diagnosis in patients with pre-existing CKD 3
• Patients with CKD may have less renal reserve, making them more vulnerable to smaller insults 1, 2
• Baseline creatinine fluctuations in CKD can make it difficult to establish the true baseline 4

Clinical Indicators of AKI on CKD

Laboratory Findings

• Sudden rise in serum creatinine from patient's baseline
• Elevated BUN (blood urea nitrogen)
• Electrolyte abnormalities (hyperkalemia, hyperphosphatemia)
• Metabolic acidosis (decreased serum bicarbonate)
• New or worsening proteinuria or hematuria 4

Clinical Manifestations

• Decreased urine output (oliguria or anuria)
• Volume overload (edema, pulmonary congestion)
• Uremic symptoms (nausea, vomiting, altered mental status) that are new or worsening compared to baseline 4

Risk Factors for AKI on CKD

• Advanced age
• Higher CKD stage (especially stages 4-5)
• Diabetes mellitus
• Heart failure
• Liver disease
• Recent exposure to nephrotoxic agents (contrast media, NSAIDs, aminoglycosides)
• Volume depletion or hemodynamic instability 4

Importance of Early Recognition

Early recognition of AKI on CKD is critical as:

• AKI severity is associated with in-hospital mortality regardless of baseline renal function 2
• AKI on CKD patients have higher mortality rates, particularly when fulfilling Stage 1 criteria or the SCr ≥3.0× criterion within Stage 3 2
• Each AKI event accelerates the decline in kidney function 5
• AKI events can trigger the transition from CKD to end-stage renal disease 6

Follow-up Recommendations

• Patients with AKI on CKD Stage 4-5 should receive nephrology consultation regardless of AKI severity 4
• Patients with Stage 3 AKI or those requiring RRT should have nephrology follow-up within 1 week of discharge 4
• Patients with persistent kidney dysfunction at discharge should have nephrology follow-up within 30 days 4
• Long-term monitoring is essential as AKI on CKD increases risk of CKD progression, cardiovascular disease, and mortality 4, 6

Early recognition and appropriate management of AKI on CKD are essential to prevent further kidney damage and improve patient outcomes.