A client is being treated for congestive heart failure.

(A) Intake and output are not laboratory tests. (B) Serum calcium levels are not affected by digoxin or furosemide. (C) Furosemide is a non–potassium-sparing loop diuretic. Hypokalemia is a common side effect of furosemide and may enhance digoxin toxicity. (D) Serum magnesium levels are not affected by digoxin or furosemide.