Pseudohyponatremia Management
Pseudohyponatremia requires no sodium correction—only treatment of the underlying condition causing the laboratory artifact. This is a measurement error, not true hyponatremia, and administering sodium replacement would be inappropriate and potentially harmful 1.
Understanding Pseudohyponatremia
Pseudohyponatremia occurs when serum sodium appears falsely low due to laboratory measurement artifacts, while the actual sodium concentration in serum water remains normal 1. This happens in three specific conditions:
- Severe hyperlipidemia - lipids occupy space in the serum sample, reducing the aqueous phase where sodium is dissolved 1, 2
- Hyperproteinemia (particularly paraproteinemia in multiple myeloma) - excess proteins create a "space-occupying lesion" that displaces serum water 1, 3
- Severe hyperglycemia - though this causes true hyponatremia through osmotic water shifts, not pseudohyponatremia 1
Diagnostic Confirmation
The key to identifying pseudohyponatremia is measuring plasma osmolality 4:
- Normal or elevated plasma osmolality with low measured sodium = pseudohyponatremia 4
- Low plasma osmolality with low sodium = true hyponatremia requiring treatment 4
Laboratory Methods to Confirm
Modern ion-selective electrode systems that directly measure sodium in undiluted samples will show normal sodium levels, while older flame photometry methods show falsely low values 3, 2. In the case report of a patient with multiple myeloma, flame photometry showed sodium of 84.5 mEq/L while ion-selective electrode measurement revealed normal sodium of 135 mEq/L 3.
Alternative confirmation methods include 2:
- Measuring serum water content via osmometry before and after dilution
- Chloride measurement before and after ultrafiltration
Management Approach
Do not administer sodium replacement - the patient's true sodium concentration is normal 1, 3. The management strategy is:
Confirm the diagnosis by checking plasma osmolality and using direct ion-selective electrode measurement if available 4, 2
Treat the underlying condition 1, 4:
- For hyperlipidemia: address the lipid disorder
- For paraproteinemia: treat the underlying plasma cell dyscrasia with chemotherapy 3
- For hyperglycemia: correct blood glucose levels
Monitor resolution - as the underlying condition improves, the laboratory artifact will resolve 3. In the multiple myeloma case, sodium measured by flame photometry normalized to 134 mEq/L one week after chemotherapy initiation, without any sodium administration 3.
Critical Pitfall to Avoid
The most dangerous error is treating pseudohyponatremia as true hyponatremia 1. Administering hypertonic saline or restricting free water when the patient's actual sodium is normal could cause iatrogenic hypernatremia and serious complications. Always verify plasma osmolality before initiating treatment for apparent hyponatremia 4.