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CDHB

Hypocalcaemia

Check albumin and if necessary adjust the calcium level. If corrected calcium is <2 mmol/L investigation is needed - provided chronic renal failure is not present. Symptoms may not be prominent if problem is long standing. Check Chvostek and Trousseau signs, and history of fits, tetany, cataracts and previous thyroid surgery.

Causes

• Hypoparathyroidism or resistance to parathyroid hormone.
• Renal failure.
• Vitamin D deficiency.
• Low magnesium states; may be caused by proton pump inhibitors, alcohol, diarrhoea etc.
• Pancreatitis, rhabdomyolysis.

Investigations

• Plasma Ca, PO₄, creatinine, Mg, ALP, alb, 25-hydroxy vitamin D and PTH levels.
• Urine calcium to creatinine ratio (preferably fasting).
• Consider malabsorption and lack of other fat soluble vitamins (A, E, and K) and assessment for osteomalacia.

Management

• If severely symptomatic:
  • Give calcium gluconate IV e.g., 10 mL of 10% solution as bolus over 2 minutes.
  • In severe cases repeated IV calcium gluconate by continuous IV infusion - e.g., 2-3 ampoules in 500 mL 5% glucose over 4-6 hours (each ampoule of 10% solution calcium gluconate contains 90 mg elemental calcium). Dose and rate is monitored by repeated checks of serum calcium. Doses of 15 mg/kg of elemental calcium over 24 hours may be needed with half of this given in the first 6 hours.
  • Start oral calcium e.g., 1000-2000 mg elemental calcium daily, e.g., calcium carbonate 1.25 g BD (500 mg calcium per tablet) or calcium carbonate effervescent (1000 mg calcium) 1-2 daily.
  • Start 1,25 dihydroxy vitamin D (calcitriol) e.g., 0.25 microgram - 1 microgram/day
  • Monitor serum calcium 12-24 hourly, aiming for corrected calcium 2 - 2.2 mmol/L. Consult Endocrinology.
  • Magnesium deficiency:
    • If severe (magnesium <0.5 mmol/L) and symptomatic, e.g., arrhythmia or tetany, consider 50 mmol magnesium IV slowly over 8-24 hours.
    • Otherwise, oral magnesium supplements 10-20 mmol/day (magnesium chelate 500 mg capsule containing 100 mg elemental magnesium (4 mmol magnesium/capsule); Mylanta suspension (6.9 mmol magnesium/10 mL)).

Topic Code: 1391