In primary adrenal insufficiency (Addison's disease), which electrolyte abnormality combination is expected due to combined glucocorticoid and mineralocorticoid deficiency?
- A Hypokalaemia, hypernatraemia, metabolic alkalosis
- B Hyperkalaemia, hypernatraemia, metabolic alkalosis
- C Hyperkalaemia, hyponatraemia, and metabolic acidosis (Type 4 RTA pattern) ✓
- D Hyponatraemia, hypokalaemia, metabolic acidosis
Explanation
In Addison's disease, both aldosterone and cortisol are deficient. Aldosterone deficiency reduces Na+ reabsorption and K+ excretion in the collecting duct, causing hyponatraemia and hyperkalaemia. Reduced H+ secretion (also aldosterone-dependent) causes metabolic acidosis (Type 4/hyperchloraemic RTA). Cortisol deficiency contributes to hyponatraemia (impaired free water excretion) and hypoglycaemia. The classic biochemical picture is hyponatraemia + hyperkalaemia + metabolic acidosis. Pigmentation, hypotension, and elevated ACTH (feedback) complete the clinical picture.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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