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Calcium and magnesium imbalances: Chvostek and Trousseau signs, tetany, seizure and ECG watch

  • Assessment

Low calcium or magnesium irritates nerves and muscles (tingling, spasms, seizures); high levels cause weakness and slow reflexes.

Updated

What it is

Calcium and magnesium keep nerves, muscles and the heart working normally. Low calcium (after parathyroid or thyroid surgery, with low vitamin D, kidney disease or high phosphorus) and low magnesium (alcohol use, poor intake, diuretics, long-term acid-suppressing medicines, diarrhoea) make nerves and muscles over-excitable: tingling around the mouth and in the hands and feet, cramps, tetany, seizures and arrhythmias. High calcium (overactive parathyroid, some cancers, immobility) causes nausea, constipation, thirst, frequent urination, weakness and confusion; high magnesium (kidney failure, magnesium-containing medicines) causes weak reflexes, slow pulse and, at worst, cardiac arrest. The nurse knows who is at risk, tests for the bedside signs, watches the rhythm and gives replacement as ordered.

Reference values

  • Calcium and magnesium are read against the laboratory's own reference range.
  • Low calcium risks: parathyroid or thyroid surgery, low vitamin D, kidney disease, high phosphorus.
  • Low magnesium risks: alcohol use, poor intake, loop diuretics, long-term proton pump inhibitors, diarrhoea, pancreatitis.
  • High calcium risks: overactive parathyroid glands, some cancers, long immobility, too much vitamin D.
  • Replacement amounts and rates: according to the order and the institutional protocol.

What you need

  • Blood pressure cuff for the Trousseau sign.
  • Cardiac monitor or ECG as ordered.
  • Seizure precautions for patients at high risk.

How to measure it (and why)

  1. Identify patients at risk, such as after thyroid or parathyroid surgery or with alcohol use — they need regular checks.
  2. Ask about tingling around the mouth and in the fingers and toes, and cramps — they are early signs of low calcium.
  3. Test the Chvostek sign by tapping the facial nerve in front of the ear — facial twitching suggests low calcium.
  4. Test the Trousseau sign with a cuff above systolic pressure for 3 minutes — hand spasm suggests low calcium.
  5. Check reflexes, strength, pulse and level of alertness — weak reflexes and a slow pulse suggest high magnesium.
  6. Monitor the rhythm or get an ECG as ordered — magnesium imbalances cause arrhythmias, and high magnesium can stop the heart.
  7. Keep seizure precautions when levels are low and symptoms appear — low magnesium can cause convulsions and low calcium tetany.
  8. Give replacement only as ordered, by the route and rate in the protocol, and recheck the level — wrong rates are dangerous.
  9. For high calcium, encourage mobility and give the IV fluids ordered — fluids are the main treatment and immobility raises calcium.

How to read it

  • Positive Chvostek or Trousseau sign, tingling or tetany: suspect low calcium.
  • Tremor, cramps, nystagmus, seizures and arrhythmias with low potassium or calcium: suspect low magnesium.
  • Nausea, constipation, thirst, frequent urination, weakness or confusion: suspect high calcium.
  • Weak reflexes, slow weak pulse and lethargy: suspect high magnesium.

Next step: when to call for help

  • Call at once for tetany or a seizure.
  • Call for tingling or a positive Chvostek or Trousseau sign, especially after neck surgery.
  • Call for a new arrhythmia, a slow pulse or weak reflexes.
  • Call for confusion, severe weakness or vomiting in a patient with high calcium.
  • Call for any result outside the range.

Test yourself

Think of the answer, then tap the question to see it.

How is the Trousseau sign tested, and what does a positive result suggest?

A blood pressure cuff is kept above systolic pressure for 3 minutes; a hand spasm suggests low calcium.

Which early symptom of low calcium does the nurse ask about after thyroid or parathyroid surgery?

Tingling or numbness around the lips and in the fingers and toes, and muscle cramps.

Which signs suggest high magnesium?

Weak reflexes, muscle weakness, lethargy and a slow, weak pulse; it can lead to cardiac arrest.

Which common causes of low magnesium does the nurse look for?

Alcohol use, poor intake, loop diuretics, long-term proton pump inhibitors, chronic diarrhoea and pancreatitis.

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Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.

Sources: Nursing Fundamentals (Open RN), 15.4 Electrolytes (Open RN, Wisconsin Technical College System (CC BY 4.0), LibreTexts, 2021); Hypercalcemia, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Magnesium deficiency, MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025).

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