Which electrolyte abnormality is most likely with chronic loop diuretic (Lasix) use?

Which electrolyte abnormality is most likely with chronic loop diuretic (Lasix) use?

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

Answer: (A)

Loop diuretics block the Na-K-2Cl transporter in the thick ascending limb, so more sodium reaches the distal nephron. In the collecting duct, the increased Na reabsorption is exchanged for potassium and hydrogen secretion, leading to potassium loss. Volume depletion from the diuresis also activates the renin-angiotensin-aldosterone system, further driving potassium excretion. Over time, this combination causes hypokalemia, which is the most likely electrolyte abnormality with chronic loop diuretic use. There can also be increased calcium and magnesium loss and, with aggressive diuresis, hyponatremia, but the hallmark change is low potassium.

Loop diuretics block the Na-K-2Cl transporter in the thick ascending limb, so more sodium reaches the distal nephron. In the collecting duct, the increased Na reabsorption is exchanged for potassium and hydrogen secretion, leading to potassium loss. Volume depletion from the diuresis also activates the renin-angiotensin-aldosterone system, further driving potassium excretion. Over time, this combination causes hypokalemia, which is the most likely electrolyte abnormality with chronic loop diuretic use. There can also be increased calcium and magnesium loss and, with aggressive diuresis, hyponatremia, but the hallmark change is low potassium.