What is expected to happen to potassium with a 0.10 change in pH?

• A. It decreases by 0.6
• B. It remains the same
• C. It increases by 0.6
• D. It changes in the same direction

Answer: (C)

Potassium shifts between inside and outside cells in response to hydrogen ion concentration. When pH falls (acidemia), hydrogen ions enter cells and potassium is pushed out to maintain electroneutrality, so extracellular potassium rises. A commonly used rough rule is that for each 0.1 unit decrease in pH, serum potassium increases by about 0.6 mEq/L. So a 0.10 change in pH that represents a drop leads to roughly a 0.6 mEq/L increase in potassium. If the pH rose instead, potassium would move into cells and fall by about the same amount. This reflects the H+/K+ exchange across cell membranes and the body's need to maintain balance.