marked elevations of either lipids or proteins in plasma can cause artifactual decreases in serum sodium because of the larger relative proportion of plasma volume that is occupied by the excess lipids or proteins
the increased protein or lipid will not appreciably change the total number of solute particles in solution
therefore the directly measured plasma osmolality will be normal
in pseudohyponatraemia no shifts of water occur
Reference:
Adrogué HJ, Tucker BM, Madias NE. Diagnosis and management of hyponatremia: a review. JAMA. 2022 Jul 19;328(3):280-91.
Zietse R. Diagnosis and treatment of hyponatremia: compilation of the guidelines. J Am Soc Nephrol. 2017 May;28(5):1340-9.
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