Hyponatremia vs. Pseudohyponatremia

Case scenario: I had a patient with MG crisis and had hyponatremia after IVIG (Na in BMP dropped from 134 to 124 on Day 4), checked at that same time serum osmolality was 269, calculated serum osmolality was 259. So is it pseudohyponatremia? What workup do I need to to differentiate pseudohyponatremia and true hyponatremia?

  1. Check ABG or VBG, the blood gas analyzer is a direct ion-specific electrode (ISE) allows measurement of plasma sodium directly from a whole-blood sample. 
  2. Calculated Serum osmolality vs measured serum osmolality, the higher the gap the more likely it is pseudohyponatremia.
  3. Calculate water content of the serum. check lipid panel and LFT for total protein Reduced % water content (<93 %) indicates pseudohyponatremia. Plasma water % = 99.1 – (1.03 × lipid concentration g/L) – (0.73 × protein concentration g/L)

Further reading:

This article explains the concept really well – why pseudohyponatremia exists? It usually depends on the lab technique they used to measure Na. https://acutecaretesting.org/en/articles/pseudohyponatremia


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s