Which electrolyte disturbance is commonly associated with loop diuretics?

• A. Hyperkalemia
• B. Hypercalcemia
• C. Hypokalemia
• D. Hypermagnesemia

Answer: (C)

Loop diuretics most commonly lead to low potassium levels because they block the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle. This inhibition reduces reabsorption of sodium, potassium, and chloride, so more sodium reaches the distal tubule. In the distal nephron, sodium reabsorption via ENaC creates a more negative luminal environment, driving potassium secretion into the urine through ROMK channels. The result is increased urinary potassium loss and a drop in plasma potassium. Volume depletion from diuresis can also activate the renin-angiotensin-aldosterone system, further increasing potassium excretion.

Other choices don’t align with the typical effect: loop diuretics don’t cause hyperkalemia; they increase potassium loss rather than retention. They also promote calcium and magnesium loss rather than elevation, so hypercalcemia or hypermagnesemia would not be expected.