The nurse is reviewing laboratory results for a group of patients. Which value should be of most concern to the nurse?

Sodium level 140 mEq/L (136-145 mEq/L)

Magnesium level 1.0 mEq/L (1.3-2.1 mEq/L)

Potassium level 3.5 mEq/L (3.5-5 mEq/L)

Calcium level 10 mg/dL (9-10.5 mg/dL)