Hypovolemic hyponatremia vs Euvolemic / hypervolemic hyponatremia
How to tell Hypovolemic hyponatremia and Euvolemic / hypervolemic hyponatremia apart when a board question makes them look alike.
First prove hypotonicity, then use volume exam: dry is hypovolemic, normal is SIADH-type euvolemic, swollen is hypervolemic.
Side by side
True hypotonic hyponatremia with clinical volume depletion: orthostasis, dry mucosa, tachycardia, low effective volume, and ADH that is appropriate for hypovolemia.
Euvolemic SIADH has concentrated urine without edema or depletion; hypervolemic hyponatremia has edema or ascites from heart failure, cirrhosis, nephrotic syndrome, or kidney failure.
Sodium and water are both lost, but sodium loss dominates; low arterial volume keeps ADH active and retains water.
SIADH retains water inappropriately; hypervolemic states retain water because effective arterial volume is low despite excess total body fluid.
Vomiting, diarrhea, diuretics, orthostasis, high urine osmolality, and low urine sodium after extrarenal loss points hypovolemic hyponatremia.
Urine osmolality above 100 with urine sodium above 40 and euvolemia points SIADH; edema/ascites/JVD points hypervolemic hyponatremia.
The trap
Low sodium does not tell volume status; urine concentration and the bedside volume exam do.
Watch it explained
The repair move
For hyponatremia, run the same sequence every time: osmolality, urine osmolality, urine sodium, volume status.
Try a free question
CoreA vomiting patient has hypotonic hyponatremia, orthostatic hypotension, dry mucous membranes, low urine sodium, and high urine osmolality from appropriate ADH. Which category is most likely?
Show answer and explanation
Answer: A. Hypovolemic hyponatremia. Hypovolemic hyponatremia has total body sodium loss exceeding water loss; low effective volume keeps ADH high.
Why the other choices are tempting
- B. SIADH is euvolemic with inappropriately concentrated urine and often urine sodium above 40.
- C. Hypervolemic hyponatremia has edema, ascites, heart failure, cirrhosis, or nephrotic clues.
- D. Primary polydipsia usually has maximally dilute urine.
- E. Pseudohyponatremia is not true hypotonic hyponatremia.
Flashcards
Tap a card to flip it.
What is the fastest separator for Hypovolemic hyponatremia vs Euvolemic / hypervolemic hyponatremia?
First prove hypotonicity, then use volume exam: dry is hypovolemic, normal is SIADH-type euvolemic, swollen is hypervolemic.
What clue should make you choose Hypovolemic hyponatremia?
True hypotonic hyponatremia with clinical volume depletion: orthostasis, dry mucosa, tachycardia, low effective volume, and ADH that is appropriate for hypovolemia.
Quick answers
What is the fastest way to tell Hypovolemic hyponatremia from Euvolemic / hypervolemic hyponatremia?
First prove hypotonicity, then use volume exam: dry is hypovolemic, normal is SIADH-type euvolemic, swollen is hypervolemic.
What is the key clue for Hypovolemic hyponatremia?
True hypotonic hyponatremia with clinical volume depletion: orthostasis, dry mucosa, tachycardia, low effective volume, and ADH that is appropriate for hypovolemia.
What is the key clue for Euvolemic / hypervolemic hyponatremia?
Euvolemic SIADH has concentrated urine without edema or depletion; hypervolemic hyponatremia has edema or ascites from heart failure, cirrhosis, nephrotic syndrome, or kidney failure.
What is the common trap with Hypovolemic hyponatremia vs Euvolemic / hypervolemic hyponatremia?
Low sodium does not tell volume status; urine concentration and the bedside volume exam do.