When initiating insulin in DKA, what potassium threshold must be met and why?

• A. Potassium threshold irrelevant; insulin raises potassium.
• B. Potassium should be ≥5.0 mEq/L before starting insulin.
• C. Potassium should be <3.0 mEq/L before starting insulin.
• D. Potassium should be ≥3.3 mEq/L before starting insulin; insulin facilitates potassium shift into cells, risking severe hypokalemia if K is low.

Answer: (D)

Potassium balance is the key idea here. In DKA, total body potassium is usually depleted from diuresis and hormonal effects, but the serum level can be normal or even high because acidosis and insulin deficiency push potassium out of cells. When you start insulin, it drives potassium back into cells as glucose is taken up and acidosis improves. That shift can cause a rapid and dangerous drop in serum potassium if there isn’t enough K+ to begin with. Therefore you want the serum potassium to be at least 3.3 mEq/L before starting insulin. If it’s below 3.3, you correct potassium first (or with insulin) until it reaches 3.3, then begin insulin and continue potassium replacement to keep K+ in a safe range (roughly 4–5).

Choosing a threshold like ≥5.0 is unnecessary and could delay insulin and correction of acidosis, while starting insulin with a potassium level below 3.3 risks severe hypokalemia. Insulin does not raise potassium; it lowers serum potassium by driving it into cells, so a low starting K+ is dangerous.