In CKD, which electrolyte abnormality is most commonly observed and why?

• A. Hyperkalemia due to reduced renal potassium excretion
• B. Hypokalemia due to dietary deficiency
• C. Hypercalcemia due to vitamin D excess
• D. Hyponatremia due to water retention

Answer: (A)

Potassium balance is tightly controlled by the kidneys, and in CKD the ability to excrete potassium falls as GFR declines and nephron number is reduced. This makes potassium accumulate in the blood. Early in CKD, remaining nephrons can compensate to some extent, but as kidney function worsens, the distal tubule’s capacity to secrete potassium diminishes, and metabolic acidosis further shifts potassium out of cells into the bloodstream. Medications that blunt aldosterone-driven potassium excretion can worsen this, but the underlying driver is reduced renal potassium excretion due to impaired kidney function. That’s why hyperkalemia is the most common electrolyte abnormality in CKD.

Hyponatremia due to water retention isn’t the defining issue in CKD, and CKD typically causes hypocalcemia from phosphate retention and reduced vitamin D activation rather than hypercalcemia. Hypokalemia would be unlikely given the impaired excretion and overall tendency toward potassium buildup.