How do I recognize, confirm, and manage pseudohypernatremia versus true hypernatremia?

Pseudohypernatremia: Recognition, Confirmation, and Management

What is Pseudohypernatremia?

Pseudohypernatremia is a laboratory artifact where measured serum sodium appears falsely elevated due to sample contamination, most commonly with trisodium citrate from catheter-lock solutions used in dialysis catheters. 1 Unlike pseudohyponatremia (which results from increased serum lipids or proteins reducing the aqueous fraction), pseudohypernatremia is almost exclusively an iatrogenic pre-analytical error. 2, 3

Recognition: When to Suspect Pseudohypernatremia

Clinical Red Flags

• Severe hypernatremia (>170 mmol/L) in an asymptomatic patient – true hypernatremia at this level causes encephalopathy, seizures, or coma 1
• Discordance between sodium level and clinical presentation – patient appears euvolemic without neurological symptoms despite critically elevated sodium 1
• Recent blood draw from a dialysis catheter or central line – especially if catheter-lock solutions (Citra-Lock™, trisodium citrate) are used 1
• Sudden, unexplained spike in sodium from previously normal values without corresponding clinical deterioration 1

High-Risk Scenarios

• Hemodialysis patients with tunneled catheters using trisodium citrate locks 1
• Blood samples drawn from the same lumen used for catheter-lock instillation 1
• Inadequate flushing or aspiration of "dead space" before sample collection 1

Confirmation: Systematic Diagnostic Approach

Step 1: Immediate Repeat Measurement

• Draw a new sample from a peripheral vein (not from the catheter) within 2 hours 1
• If sodium normalizes (typically 135-145 mmol/L), pseudohypernatremia is confirmed 1
• If elevated sodium persists with appropriate clinical symptoms, treat as true hypernatremia 1

Step 2: Verify with Alternative Analyzer

• Measure sodium on a different analyzer using the same sample 1
• Concordant results across platforms suggest true hypernatremia, while discordant results point to analytical interference 1
• Direct ion-selective electrode (ISE) methods are less susceptible to interference than indirect ISE 2, 3

Step 3: Evaluate Sample Collection Technique

• Review the blood draw procedure systematically: 1
  • Was sample drawn from a catheter with lock solution?
  • Was adequate volume discarded before collection (minimum 5-10 mL)?
  • Was the catheter flushed appropriately before sampling?
• Check for visible contamination – trisodium citrate may cause sample clotting or unusual appearance 1

Step 4: Calculate Expected Sodium Change

• True hypernatremia develops gradually – acute rises >10-15 mmol/L in hours without corresponding clinical deterioration are suspicious 1
• Assess volume status and urine output – true hypernatremia shows signs of dehydration or diabetes insipidus 4

Management Algorithm

If Pseudohypernatremia is Confirmed

1. Do NOT treat the sodium level – no hypertonic fluid correction is needed 1
2. Document the error in the medical record to prevent repeated unnecessary interventions 1
3. Educate nursing and phlebotomy staff on proper catheter sampling technique 1
4. Implement protocol changes: 1
   • Always discard adequate dead-space volume (≥10 mL) before blood draw
   • Preferentially draw labs from peripheral veins when possible
   • Label samples drawn from catheters to alert laboratory staff
5. Recheck sodium from peripheral vein to establish true baseline 1

If True Hypernatremia is Confirmed

Treat based on severity and underlying cause: 4

• Mild hypernatremia (146-150 mmol/L): Increase oral free water intake; address underlying cause 4
• Moderate hypernatremia (151-160 mmol/L): Oral or IV hypotonic fluids (0.45% saline or D5W); correct at 0.5 mmol/L/hour maximum 4
• Severe hypernatremia (>160 mmol/L): IV hypotonic fluids with close monitoring; correct no faster than 10-12 mmol/L per 24 hours to avoid cerebral edema 4

Key Differences: Pseudohypernatremia vs. Pseudohyponatremia

Feature	Pseudohypernatremia	Pseudohyponatremia
Mechanism	Sample contamination with sodium-containing solutions [1]	Increased serum lipids/proteins reducing aqueous fraction [2,3]
Frequency	Rare, iatrogenic [1]	More common in hyperlipidemia, hyperproteinemia [2,3,5]
Detection	Repeat sample from different site [1]	Direct ISE measurement or serum water content [2,3]
Clinical significance	None – purely artifactual [1]	May reflect underlying metabolic disorder [5]
Modern analyzers	Not prevented by current technology [1]	Largely eliminated by direct ISE methods [3]

Common Pitfalls to Avoid

• Treating severe "hypernatremia" without confirming the diagnosis – can lead to unnecessary and potentially harmful interventions 1
• Assuming all analyzer results are accurate – severe discordance with clinical picture mandates repeat testing 1
• Drawing labs from catheters without adequate dead-space discard – the most common cause of pseudohypernatremia 1
• Failing to communicate with laboratory staff about sample source and collection technique 1
• Not documenting pseudohypernatremia in the record – risks repeated misinterpretation and inappropriate treatment 1

Prevention Strategies

Implement standardized catheter sampling protocols: 1

• Discard minimum 10 mL before blood draw from any catheter
• Use peripheral venipuncture for critical lab values when feasible
• Label all catheter-drawn samples clearly
• Educate staff on catheter-lock solutions and contamination risk

Maintain high clinical suspicion when sodium values are discordant with patient presentation, especially in dialysis patients with central catheters 1