Acute hypocalcaemia can be life threatening, necessitating urgent treatment. In severe cases, intravenous calcium forms the mainstay of initial therapy, but it is essential to ascertain the underlying cause and commence specific therapy as early as possible. This guideline aims to take the non-specialist through the initial phase of assessment and management.
Symptoms of hypocalcaemia typically develop when adjusted serum calcium levels fall below ~1.9 mmol/L. However, this threshold varies greatly and is dependent on the rate of fall.
Symptoms and signs of hypocalcaemia include:
- Peri-oral and digital paraesthesiae
- Positive Trousseau’s and Chvostek’s signs
- Tetany and carpopedal spasm
- ECG changes (prolonged QT interval) and arrhythmia
The most common cause of acute symptomatic hypocalcaemia in hospital practice is disruption of parathyroid gland function due to total thyroidectomy. Hypocalcaemia may be temporary or permanent.
Other causes include:
- Following selective parathyroidectomy (hypocalcaemia is usually transient and mild)
- Severe vitamin D deficiency
- Mg2+ deficiency (consider PPI-associated hypomagnesaemia)
- Cytotoxic drug-induced hypocalcaemia
- Pancreatitis, rhabdomyolysis and large volume blood transfusions
- Serum calcium (adjusted for albumin)
- Parathyroid hormone (PTH)
- Urea and electrolytes
- Vitamin D
‘Mild’ hypocalcaemia: asymptomatic; serum calcium >1.9 mmol/L.
- Commence oral calcium supplements such as Sandocal 1000, 2 tablets BD (Alternatives include Adcal 3 tablets BD, Cacit 4 tablets BD, or Calcichew Forte 2 tablets BD).
- If post-thyroidectomy and patient asymptomatic, repeat calcium 24 h later:
- If vitamin D deficiency is the cause, commence vitamin D supplementation: load with ~300,000 units of cole- or ergocalciferol over ~6–10 weeks
- If hypomagnesaemia-related, stop any precipitating drug and administer i.v. Mg2+, 24 mmol/24 h, made up as 6 g of MgSO4 (30 mL of 20%, 800 mmol/L, MgSO4) in 500 mL Normal saline or 5% dextrose. Monitor serum Mg2+ and aim to achieve normal serum magnesium level
- If other cause of hypocalcaemia, treat underlying condition.
Severe hypocalcaemia: serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range.
- This is a medical emergency
- Administer i.v. calcium gluconate
- Initially, give 10–20 mL 10% calcium gluconate in 50–100 mL of 5% dextrose i.v. over 10 min with ECG monitoring. This can be repeated until the patient is asymptomatic. It should be followed up with a calcium gluconate infusion as follows:
- Treat the underlying cause; in post-operative hypocalcaemia and other cases of hypoparathyroidism, this consists of alfacalcidol or calcitriol therapy. Starting doses should be approximately 0.25–0.5 micrograms per day
- Vitamin D deficiency or hypomagnesaemia should be treated as described above
Hazards of i.v. calcium administration
Uncommon, but include local thrombophlebitis, cardiotoxicity, hypotension, calcium taste, flushing, nausea, vomiting and sweating. Patients with cardiac arrhythmias or on digoxin therapy need continuous ECG monitoring during i.v. calcium replacement.
For patients commenced on alfacalcidol or calcitriol, monitoring of adjusted serum calcium levels should initially be performed approximately one week post discharge, then if satisfactory at one, three and then six months. Follow-up by a specialist with an interest in calcium disorders is recommended.
The document should be considered as a guideline only; it is not intended to determine an absolute standard of medical care. The doctors concerned must make the management plan for an individual patient.