In suspected primary aldosteronism, which laboratory finding supports the diagnosis?

• A. Hyperkalemia
• B. Hypokalemia
• C. Hyponatremia
• D. Metabolic acidosis

Answer: (B)

Excess aldosterone drives sodium reabsorption and, at the same time, increases potassium and hydrogen ion excretion in the distal nephron. The net effect is a drop in serum potassium (hypokalemia) and often a metabolic alkalosis. This hypokalemia is the lab finding that most strongly supports suspected primary aldosteronism. You may also see a suppressed renin level with an inappropriately high aldosterone-to-renin ratio. The other options don’t fit: hyperkalemia isn’t typical with aldosterone excess, hyponatremia isn’t a hallmark, and metabolic acidosis would not be expected given the potassium shifts toward alkalosis.