Loop diuretics commonly cause which electrolyte disturbance?

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

Answer: (C)

Loop diuretics block the Na+-K+-2Cl− transporter in the thick ascending limb of the loop. This prevents reabsorption of sodium, potassium, and chloride, so more sodium reaches the distal nephron. In the collecting duct, the increased sodium delivery stimulates potassium (and hydrogen) secretion, especially under the influence of aldosterone, leading to more potassium waste in the urine and a lower potassium level in the blood. The result is hypokalemia, a common electrolyte disturbance with loop diuretics. This mechanism also explains why hyperkalemia isn’t typical here, while hyponatremia and hypercalcemia are not the characteristic changes—loops actually increase calcium excretion, which can trend toward lower calcium rather than higher.