Why must potassium be checked before giving insulin for diabetic ketoacidosis?

Potassium must be checked before insulin administration in diabetic ketoacidosis because insulin drives potassium from the blood into cells. During DKA, serum potassium may appear normal or even elevated due to acidosis shifting potassium out of cells, but total body potassium is actually depleted from urinary losses. Giving insulin without correcting low potassium can cause life-threatening hypokalemia leading to cardiac arrhythmias and respiratory muscle paralysis.