The nurse is caring for a client with a critically high potassium level. The client has received sodium polystyrene sulfonate (Kayexalate). The nurse determines the medication's effectiveness if the client's repeat serum potassium level is:

Rationale: A. A potassium level of 4.9 mEq/L is within the normal reference range (typically 3.5–5.0 mEq/L), indicating that the hyperkalemia has been successfully corrected. B. A potassium level of 5.5 mEq/L is still above normal and does not suggest full effectiveness of the treatment. C. A potassium level of 6.2 mEq/L remains critically high and indicates that the medication was not effective. D. A potassium level of 5.8 mEq/L is still elevated and may continue to pose cardiac risks, suggesting partial or no effectiveness.