What is the normal potassium range in mEq/L?

• A. 2.5-4.0 mEq/L
• B. 3.5-5.0 mEq/L
• C. 4.5-5.5 mEq/L
• D. 5.0-6.0 mEq/L

Answer: (B)

Potassium in the blood is kept within a tight window because even small shifts can affect heart rhythm and muscle function. The standard adult serum potassium range used in most labs is about 3.5 to 5.0 mEq/L. This range reflects the balance between potassium inside cells and in the extracellular fluid, maintained by the kidneys (excretion) and by cellular processes (insulin, catecholamines, and hormonal regulation).

Why this range is the best fit: values below 3.5 (hypokalemia) can cause weakness and dangerous heart rhythm changes, while values above 5.0 (hyperkalemia) can also disrupt cardiac conduction and lead to life-threatening arrhythmias. The other options either set the lower end too high or the upper end too low, which would misclassify many normal readings as abnormal.

So, 3.5 to 5.0 mEq/L is the normal range.