After IV insulin and dextrose for hyperkalemia therapy, which laboratory value should improve first?

• A. Serum potassium
• B. Serum bicarbonate
• C. Serum calcium
• D. Serum sodium

Answer: (A)

Potassium falls first because insulin drives potassium into cells via the Na+/K+-ATPase pump. When IV insulin with glucose is given for hyperkalemia, the extracellular potassium is pulled into cells very quickly, usually within minutes to an hour, so the serum potassium level drops before other electrolytes or values change. The other labs reflect different processes or later effects: bicarbonate depends on acid-base status, calcium isn’t directly affected by this acute insulin therapy, and sodium shifts can occur with fluids but don’t mirror the immediate potassium-lowering action. So, the first lab value to improve is serum potassium.