What is the management of pseudohyponatremia?

Management of Pseudohyponatremia

Pseudohyponatremia requires no specific treatment directed at sodium levels as it represents a laboratory artifact rather than a true electrolyte disturbance.

What is Pseudohyponatremia?

Pseudohyponatremia is a laboratory artifact characterized by falsely low serum sodium measurements in the presence of normal plasma tonicity. Unlike true hyponatremia, it does not cause water movement across cell membranes and has no clinical manifestations of hypotonic hyponatremia 1.

Mechanisms of Pseudohyponatremia

Pseudohyponatremia occurs when sodium is measured using indirect ion-selective electrode (I-ISE) methods that require dilution of the sample prior to measurement. Three key mechanisms are responsible:

1. Electrolyte exclusion effect: Elevated serum solids (proteins or lipids) reduce the proportion of serum water, causing reciprocal depression in measured sodium values 1
2. Dilution effect: Increased water concentration post-dilution compared to normal serum
3. Viscosity interference: Hyperviscosity reduces serum delivery to the measuring device 1

Diagnosis of Pseudohyponatremia

Clinical Scenarios to Consider Pseudohyponatremia

• Low serum sodium with normal plasma osmolality
• Absence of symptoms typically associated with hyponatremia
• Presence of conditions associated with hyperlipidemia or hyperproteinemia:
  • Severe hyperlipidemia
  • Multiple myeloma
  • Monoclonal gammopathies
  • Hyperproteinemia from any cause
  • HIV and hepatitis C coinfection (due to hypergammaglobulinemia) 2

Diagnostic Approach

1. Measure serum osmolality: Normal serum osmolality (280-295 mOsm/kg) with low sodium suggests pseudohyponatremia
2. Check for elevated serum proteins or lipids
3. Compare sodium measurements: If available, compare results from direct ion-specific electrode (D-ISE) with indirect ISE methods 3
4. Calculate osmolal gap: An elevated osmolal gap may be present due to the falsely lowered sodium level leading to a falsely low calculated serum osmolality 2

Management of Pseudohyponatremia

Key Principles

1. No sodium correction needed: Pseudohyponatremia does not require treatment to address the sodium level 1
2. Avoid sodium correction: Attempting to correct sodium levels can be potentially harmful as the patient does not have true hyponatremia 1
3. Address underlying cause: Treat the condition causing hyperproteinemia or hyperlipidemia if clinically indicated

Laboratory Considerations

• Know which method your laboratory uses for sodium measurement
• Request direct ISE measurement when pseudohyponatremia is suspected
• Consider using the PWC (plasma water content) determination method to accurately assess true sodium concentration 3

Clinical Pitfalls to Avoid

1. Misdiagnosis: Confusing pseudohyponatremia with true hyponatremia can lead to inappropriate treatment
2. Inappropriate treatment: Administering hypertonic saline or fluid restriction for pseudohyponatremia is unnecessary and potentially harmful
3. Missing the underlying cause: Failure to identify and address conditions causing elevated proteins or lipids
4. Laboratory method confusion: Not knowing which method your laboratory uses for sodium measurement 4

Distinguishing from True Hyponatremia

Unlike pseudohyponatremia, true hyponatremia (serum sodium <130 mmol/L) may require specific management based on volume status:

• Hypovolemic hyponatremia: Rehydration with isotonic saline 5
• Hypervolemic hyponatremia: Fluid restriction and treatment of underlying cause 6
• Euvolemic hyponatremia: Free water restriction and addressing underlying cause 5

Remember that pseudohyponatremia is a laboratory artifact, not a true electrolyte disorder requiring correction of sodium levels.