skip to main content

Hypovolaemic Hypernatraemia — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

EasyNephrologyHypovolaemic HypernatraemiaRACP Adult Medicine

A 75-year-old nursing home resident with dementia is found obtunded. She has dry mucous membranes, reduced skin turgor, tachycardia, and hypotension. Na⁺ is 162 mmol/L. Urine osmolality is 800 mOsm/kg (appropriately concentrated). Urine Na⁺ is <10 mmol/L. What is the most likely cause?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Hypovolaemic hypernatraemia (inadequate water intake)

Hypernatraemia with hypovolaemia (dry mucosa, tachycardia, hypotension), appropriately concentrated urine (intact ADH and renal concentrating ability), and low urine Na⁺ (renal sodium avidity) in a demented elderly patient is hypovolaemic hypernatraemia from inadequate water intake. This is the most common cause of hypernatraemia. Treatment: free water replacement (oral/NG if possible, IV 5% dextrose). Correct slowly (<10 mmol/L/24 hours to avoid cerebral oedema).

Reference: eTG – 2024 – Hypernatraemia; KDIGO 2024