In Assessing a Patient Before Administration of a Cardiac Glycoside

In assessing a patient before administration of a cardiac glycoside, the nurse knows that which lab result can increase the toxicity of the drug?

A) Potassium level 2.8 mEq/L
B) Potassium level 4.9 mEq/L
C) Sodium level 140 mEq/L
D) Calcium level 10 mg/dL