Which electrolyte is most likely to be decreased by loop diuretics?

• A. Calcium
• B. Potassium
• C. Magnesium
• D. Chloride

Answer: (B)

Loop diuretics block the Na+-K+-2Cl− transporter in the thick ascending limb of the loop of Henle, so more sodium, chloride, and potassium stay in the tubule to be excreted. The increased delivery of sodium to the distal nephron promotes potassium secretion into the urine, especially under aldosterone’s influence, leading to potassium loss. This makes potassium the electrolyte most likely to decrease with loop diuretics. They also raise calcium and magnesium excretion due to loss of the lumen-positive charge, but the most clinically notable change is the drop in potassium. Monitor potassium closely to prevent hypokalemia and potential arrhythmias, and manage with potassium-sparing strategies if needed.