- Have a screening or baseline serum Na < 130 mEq/l or > 145 mEq/l; a serum K < 3.5 mEq/l or > 5.5 mEq/l; a serum Ca < 7.5 mg/dl or > 10.2 mg/dl; or a serum Mg < 1.6 mEq/l or > 3.0 mEq/l., or a digoxin level above 1ng/ml