In diabetic ketoacidosis, why can serum potassium be high at presentation despite total body potassium depletion?

• A. Acidosis and insulin deficiency cause K+ shift out of cells
• B. Insulin therapy causes K+ excretion
• C. Ketone bodies bind potassium
• D. Renal potassium loss due to diuresis

Answer: (A)

In diabetic ketoacidosis the serum potassium can be high at presentation because insulin deficiency and acidosis cause potassium to move out of cells into the bloodstream. Insulin normally drives potassium into cells, so when there isn’t enough insulin, potassium stays outside cells. At the same time, the acidosis pushes hydrogen ions into cells in exchange for potassium leaving the cells to help maintain electrical balance. The net effect is a higher potassium level in the blood even though total body potassium stores are actually depleted from ongoing urinary and GI losses. When treatment starts, insulin and shifting pH back toward normal drive potassium back into cells, which can precipitate a drop in serum potassium if it isn’t replenished.

Why the other ideas don’t explain the presentation as well: insulin therapy would lower serum potassium by moving it into cells, not raise it; ketone bodies don’t bind potassium to raise its serum level; and while renal potassium loss from diuresis contributes to total body depletion, it doesn’t account for an elevated serum potassium seen initially.