High Magnesium in Renal Failure: What to Monitor

Renal & Electrolytes · Question from the ATI RN Medical-Surgical 2023 Proctored Exam study set

Correct answer: B. Diminished DTRs

Why this is the answer

A magnesium level of 3.2 mEq/L is elevated (hypermagnesemia), and excess magnesium acts as a CNS depressant — it blunts neuromuscular transmission, producing diminished deep tendon reflexes (DTRs), along with bradycardia and hypotension. Hyperactive reflexes (A) would suggest low, not high, magnesium (or low calcium). Tachycardia (C) is the opposite of what hypermagnesemia produces — it slows the heart rate instead. Hypertension (D) is also backwards, since magnesium's vasodilating, CNS-depressant effect tends to lower blood pressure.

The bigger concept

Magnesium and calcium behave similarly on the neuromuscular system: too much of either depresses excitability (diminished reflexes, weakness, and in severe cases respiratory depression), while too little causes irritability (hyperactive reflexes, tetany, seizures). Renal failure patients are prone to hypermagnesemia because failing kidneys can't excrete the excess.

Related Renal & Electrolytes practice questions

• Positive Trousseau's Sign: What It Means
• Why Anemia Is Common in Chronic Renal Failure
• Defining the Oliguric Phase of Acute Renal Failure
• Furosemide and Potassium Loss
• Managing High Phosphorus in Chronic Renal Failure

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