What labs should be checked to determine if an Acute Kidney Injury (AKI) patient can discontinue dialysis?

Laboratory Tests to Determine Discontinuation of Dialysis in AKI Patients

Urine output is the most reliable and robust predictor for successful discontinuation of renal replacement therapy (RRT) in AKI patients, with a sensitivity of 66.2% and specificity of 73.6%. 1

Primary Laboratory Parameters to Monitor

Essential Parameters

• Urine output: The most studied and validated parameter for RRT discontinuation

  • Higher urine output at the time of RRT cessation correlates with successful discontinuation 1
  • Should be monitored daily during RRT and prior to consideration for discontinuation
  • While no single threshold has been established, increasing urine output is a positive prognostic sign

• Serum creatinine:

  • Weekly assessment of serial pre-dialysis serum creatinine values 2
  • Spontaneous reduction in creatinine combined with adequate urine output suggests recovery 3
  • Should be measured daily when considering RRT discontinuation

• BUN (Blood Urea Nitrogen):

  • Should be monitored daily alongside creatinine 2
  • Trends are more important than absolute values

Electrolyte and Acid-Base Parameters

• Serum electrolytes:

  • Potassium, phosphate, and magnesium should be determined frequently 2
  • Normalization without dialysis support suggests improving kidney function
  • Hyperkalemia resolution is particularly important before discontinuing RRT

• Acid-base status:

  • Serum CO₂/bicarbonate levels should be monitored 2
  • Resolution of metabolic acidosis without RRT suggests improving kidney function

Advanced Biomarkers

While traditional parameters remain the mainstay, newer biomarkers may provide additional information:

• Serum cystatin C:

  • Higher values at RRT discontinuation independently predict chronic dialysis dependence 1
  • More sensitive than creatinine for early detection of kidney function changes

• Serum NGAL (Neutrophil Gelatinase-Associated Lipocalin):

  • Predictive of successful CRRT discontinuation in non-septic AKI patients 1
  • Less reliable in patients with sepsis-associated AKI

• Inflammatory markers:

  • Elevated IL-6, IL-8, IL-10, IL-18, TNFR-I, and TNFR-II are associated with lower kidney recovery 1
  • Consider in complex cases, though not routinely recommended

Decision-Making Algorithm

1. Daily assessment of:

   • Urine output (primary parameter)
   • Serum creatinine and BUN trends
   • Electrolyte balance (particularly potassium)
   • Acid-base status

2. Consider RRT discontinuation when:

   • Patient is passing >1L urine/24h 3
   • Spontaneous reduction in creatinine is observed 3
   • Electrolyte and acid-base abnormalities are resolving without RRT
   • Hemodynamic stability is achieved

3. After RRT discontinuation:

   • Laboratory and clinical evaluation should occur within 3 days (no later than 7 days) 2
   • Monitor for rebound increases in creatinine, BUN, or electrolyte abnormalities
   • Be prepared to resume RRT if necessary

Important Clinical Considerations

• Combined assessment: Using multiple parameters together (urine output, creatinine, and electrolytes) provides better predictive accuracy than any single parameter 1

• Timing of evaluation: Organ recovery is defined as sustained independence from RRT for at least 14 days 2

• Pitfalls to avoid:

  • Relying solely on serum creatinine, which can be misleading in critically ill patients due to muscle wasting
  • Failing to account for diuretic use when interpreting urine output 2
  • Discontinuing RRT too early, which may necessitate reinitiation and potentially worsen outcomes
  • Overlooking the need for regular post-discontinuation monitoring

• Special considerations:

  • In patients with sepsis, urine output is a more significant predictor than biomarkers 1
  • Patients with pre-existing CKD may have different recovery patterns and thresholds

By systematically monitoring these parameters, clinicians can optimize the timing of RRT discontinuation to improve patient outcomes and reduce unnecessary continuation of dialysis.