Which condition is associated with isotonic hyponatremia?

Isotonic hyponatremia refers to a situation where the serum sodium concentration is low, but the serum osmolality is normal due to the presence of other substances in the serum that dilutes sodium. One condition that can lead to isotonic hyponatremia is hyperlipidemia. In hyperlipidemia, the elevated levels of lipids in the blood can cause a decrease in the sodium concentration when measured, because the increased lipid content can interfere with the standard sodium assessment methods, resulting in a dilutional effect that appears as low sodium levels when, in fact, the serum osmolality is within the normal range.

Hyperglycemia, acute kidney injury, and renal artery stenosis generally lead to hypotonic hyponatremia due to different pathophysiological mechanisms. Hyperglycemia may cause dilutional hyponatremia by raising serum osmolality, which pulls water into the bloodstream and can cause a net decrease in sodium concentration as well. Acute kidney injury and renal artery stenosis can both affect kidney function and electrolyte handling, typically leading to variations in sodium absorption or excretion that correspond with hypotonic hyponatremia, rather than isotonic.