What is the normal serum potassium range?

• A. 2.5-4.0 mEq/L
• B. 4.0-5.5 mEq/L
• C. 3.0-4.5 mEq/L
• D. 3.5-5.0 mEq/L

Answer: (D)

Normal serum potassium is typically 3.5 to 5.0 mEq/L. Potassium helps set the resting membrane potential for nerves and muscles, especially the heart, so small shifts can affect conduction and rhythm. The kidneys regulate potassium balance, with hormones like aldosterone promoting excretion when levels are high. Values below 3.5 (hypokalemia) can cause weakness, cramps, and arrhythmias; values above 5.0 (hyperkalemia) can lead to dangerous conduction abnormalities. Among the options, the 3.5-5.0 mEq/L range is the standard reference interval used in most labs. The other ranges either lower the lower limit or raise the upper limit beyond the typical reference, so they’re not the conventional normal range.