A 55-year-old woman admitted with pancreatitis has serum sodium of 122 mEq/L, but plasma appears visibly milky and triglycerides are 1800 mg/dL. Measured plasma osmolality is 288 mOsm/kg. The correct interpretation of her sodium value is:

• A True hyponatremia requiring hypertonic saline
• B Translocational hyponatremia due to hyperglycemia
• C Dilutional hyponatremia due to SIADH
• D Pseudohyponatremia due to displacement of plasma water by lipid ✓

Explanation

Severe hypertriglyceridemia occupies plasma volume and displaces water, so sodium is measured in a smaller aqueous phase and reads falsely low. True plasma osmolality and tonicity are normal, hence no treatment for hyponatremia is needed. SIADH gives true hypo-osmolality, and translocational hyponatremia requires hyperglycemia, neither of which fits this picture.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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