The Model for End-stage Liver Disease (MELD-Na) score includes serum sodium as it independently predicts mortality. A patient with MELD score 20 (by original MELD) and serum Na 125 mEq/L would have MELD-Na of approximately 30. This is because hyponatraemia in cirrhosis reflects:
- A Salt-wasting nephropathy from hepatorenal syndrome
- B Dilutional hypervolaemic hyponatraemia due to excess ADH from non-osmotic stimuli ✓
- C SIADH from liver metastases
- D Free water loss exceeding sodium loss
Correct answer: B. Dilutional hypervolaemic hyponatraemia due to excess ADH from non-osmotic stimuli
Explanation
Hyponatraemia in cirrhosis is dilutional and hypervolaemic. Splanchnic vasodilatation reduces effective arterial blood volume, non-osmotically stimulating baroreceptors and causing excess ADH (arginine vasopressin) secretion. ADH causes free water retention despite already expanded total body water (ascites, oedema). Na <130 mEq/L in cirrhosis predicts poor prognosis independent of MELD, leading to MELD-Na incorporation (OPTN, 2016). Tolvaptan (V2 receptor antagonist) can correct hyponatraemia but does not improve survival.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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