What is the difference between acute kidney injury (AKI) and chronic kidney disease (CKD)?

Differences Between Acute Kidney Injury and Chronic Kidney Disease

The primary difference between acute kidney injury (AKI) and chronic kidney disease (CKD) is their duration: AKI occurs rapidly over less than 7 days, while CKD represents kidney dysfunction persisting for more than 3 months, with acute kidney disease (AKD) bridging the gap between them from 7 days to 3 months. 1, 2

Definitions and Diagnostic Criteria

Acute Kidney Injury (AKI)

• Defined as an abrupt decrease in kidney function occurring over 7 days or less 1
• Diagnosed using KDIGO criteria: increase in serum creatinine ≥0.3 mg/dL within 48 hours, or increase ≥50% within 7 days, or urine output <0.5 mL/kg/h for 6 hours 3
• Can be staged (1,2, and 3) based on severity, with hospital mortality increasing progressively with each stage 3
• May be classified as transient (recovery within 48-72 hours) or persistent (continuing beyond 48-72 hours) 1

Chronic Kidney Disease (CKD)

• Defined by markers of kidney damage or decreased glomerular filtration rate (GFR) persisting for >3 months 1
• Classified according to cause, GFR, and albuminuria criteria (CGA classification) 1, 2
• Progression is typically gradual and often irreversible 4
• Associated with long-term complications including cardiovascular disease, mineral bone disorders, and anemia 2

Acute Kidney Disease (AKD)

• Bridges the gap between AKI and CKD, representing kidney dysfunction present for 7 days to 3 months 1, 5
• Includes patients with persistent AKI and those with kidney damage not meeting AKI criteria 1
• Nearly three times more prevalent than AKI and associated with increased risk of death and CKD development/progression 1

Pathophysiology and Causes

Acute Kidney Injury

• Often caused by prerenal (decreased kidney perfusion), intrinsic renal (direct kidney damage), or postrenal (urinary tract obstruction) factors 6
• Characterized by rapid onset and potentially reversible nature 3
• Common causes include sepsis, nephrotoxic medications, volume depletion, and urinary obstruction 6

Chronic Kidney Disease

• Results from progressive, irreversible damage to nephrons over time 2
• Common causes include diabetes, hypertension, glomerulonephritis, and polycystic kidney disease 2
• Characterized by gradual loss of kidney function with progressive fibrosis 4

Management Approaches

Acute Kidney Injury Management

• Focuses on identifying and treating the underlying cause 6
• Immediate interventions include:
  • Discontinuing nephrotoxic agents 2
  • Ensuring appropriate volume status and perfusion pressure 2
  • Close monitoring of serum creatinine and urine output 3
  • Renal replacement therapy if indicated for severe cases 3

Chronic Kidney Disease Management

• Emphasizes long-term strategies to slow progression 2
• Key approaches include:
  • Cause-specific treatment 2
  • Blood pressure control, often with ACEi or ARB therapy for patients with hypertension and proteinuria 2
  • Management of metabolic complications (anemia, mineral bone disorders) 2
  • Preparation for renal replacement therapy when approaching end-stage kidney disease 2

Relationship Between AKI and CKD

• AKI and CKD form a bidirectional relationship where each can lead to or worsen the other 4
• AKI increases the risk of developing or worsening CKD, particularly with:
  • Higher stages of AKI 4
  • Multiple episodes of AKI 4
  • Pre-existing CKD 4
• CKD is a significant risk factor for developing AKI 4

Common Pitfalls in Clinical Practice

• Failing to recognize AKD as a distinct entity bridging AKI and CKD 1, 7
• Not adjusting medication dosing appropriately during transitions between AKI, AKD, and CKD 2
• Overlooking the need for follow-up after AKI episodes, which increases the risk of progression to CKD 7
• Using dual RAAS blockade, which increases hyperkalemia and AKI risk 2
• Failing to consider kidney biopsy in cases of unexplained AKI/AKD, which may reveal underlying glomerular pathology 8

Monitoring and Follow-up

• As GFR stabilizes after AKI, transition from AKI-based staging to GFR-based categories 2
• Consider using measured GFR rather than estimated GFR when kidney function is changing rapidly 2
• Monitor for maladaptive repair mechanisms that may accelerate progression to CKD 2
• Early and regular follow-up by a nephrologist for patients with AKD 5