Normal adult serum potassium range?

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

Answer: (C)

Potassium balance is tightly regulated because it sets the excitability of nerves and muscles, including the heart. In adults, the normal serum potassium level is roughly three and a half to five milliequivalents per liter. This narrow window means values outside this range can disrupt conduction and muscle function: too little potassium lowers excitability and can cause weakness, cramping, and dangerous heart rhythms; too much potassium increases the risk of life-threatening arrhythmias. When you review lab results, compare the value to this reference range, keeping in mind that some labs use slightly different cutoffs. The other ranges fall outside the typical normal span: some are too low at the bottom, some are too high at the top, making them not safely representative of normal potassium levels.