Hypokalemia due to gastrointestinal loss

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Loss of potassium through the gastrointestinal tract is a classic cause of hypokalemia. The stool and GI secretions contain potassium, and when they are lost in large amounts—as in profuse diarrhea—the body's potassium stores are depleted. Vomiting also leads to potassium loss, and the associated volume depletion stimulates mechanisms (like increased aldosterone activity) that promote renal potassium excretion, further lowering serum potassium.

Other conditions listed can cause low potassium, but not primarily through GI losses. Cushing’s syndrome can cause potassium loss via a cortisol-driven mineralocorticoid effect; hyperaldosteronism increases renal potassium excretion; renal tubular acidosis causes potassium loss through renal handling of acid-base balance. The key point here is that both diarrhea and vomiting directly deplete potassium through GI fluid losses.