Question:hard
All of the following statements about hyponatremia are true, except:
All of the following statements about hyponatremia are true, except:
Show Hint
Pseudohyponatremia has normal plasma osmolality, not low.
Updated On: Jun 24, 2026
- Pseudohyponatremia is associated with low plasma osmolality
- Hyponatremia associated with hyperglycemia has high plasma osmolality
- Hyponatremia associated with SIADH is normovolemic
- NSAIDs increase the potency of vasopressin
Show Solution
The Correct Option is A
Solution and Explanation
The smart way through this is to bin each form of hyponatremia by plasma osmolality, since that is what separates the real thing from the fakes.
Pseudohyponatremia is a measurement artefact. When plasma is loaded with fat or protein, the watery part that actually holds sodium shrinks, so the lab number looks low while true sodium activity is unchanged. Crucially, the osmolality in this situation is normal. Option A calls it low, which is incorrect, making it the answer.
Check the others. With high blood glucose, sugar drags water out of cells into the bloodstream and dilutes sodium, and the same glucose pushes osmolality up, so that hyponatremia is hyperosmolar, matching option B. In SIADH the body holds onto water but does not become fluid overloaded or depleted, leaving the patient euvolemic, so option C is right. NSAIDs knock out prostaglandins, which normally counteract vasopressin in the kidney; with that brake removed, vasopressin acts more powerfully to retain water, so option D is right.
So the one wrong line is the claim that pseudohyponatremia carries a low osmolality, when it is in fact normal.
\[\boxed{\text{Pseudohyponatremia is associated with low plasma osmolality}}\]
Pseudohyponatremia is a measurement artefact. When plasma is loaded with fat or protein, the watery part that actually holds sodium shrinks, so the lab number looks low while true sodium activity is unchanged. Crucially, the osmolality in this situation is normal. Option A calls it low, which is incorrect, making it the answer.
Check the others. With high blood glucose, sugar drags water out of cells into the bloodstream and dilutes sodium, and the same glucose pushes osmolality up, so that hyponatremia is hyperosmolar, matching option B. In SIADH the body holds onto water but does not become fluid overloaded or depleted, leaving the patient euvolemic, so option C is right. NSAIDs knock out prostaglandins, which normally counteract vasopressin in the kidney; with that brake removed, vasopressin acts more powerfully to retain water, so option D is right.
So the one wrong line is the claim that pseudohyponatremia carries a low osmolality, when it is in fact normal.
\[\boxed{\text{Pseudohyponatremia is associated with low plasma osmolality}}\]
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