Hypocalcaemia

• There are multiple causes of hypocalcaemia that are broadly be divided into four groups:

  • Hypocalcaemia with raised PTH 
  • Hypocalcaemia with low PTH 
  • Hypocalcaemia related to magnesium metabolism
  • Medication-induced hypocalcaemia
• Low magnesium is a common cause of hypocalcaemia because it impairs the action of PTH leading to resistance. In severe hypomagnesaemia it can cause a reduction in PTH secretion
• Hypocalcaemia and raised PTH:

  • Vitamin D deficiency
  • Chronic kidney disease - reduced activation of vitamin D and reduced renal absorption of calcium
  • Pseudohypoparathyroidism -resistance to PTH
• Hypocalcaemia and low PTH:

  • Most commonly due to surgery on the neck e.g. thyroidectomy - usually transient
  • Hypoparathyroidism - most commonly immune-mediated destruction of the parathyroid glands
• Hypocalcaemia is defined as a serum corrected calcium concentration < 2.2 mmol/L.
• Untreated, hypocalcaemia can cause dangerous cardiac arrhythmias and seizures

  Acute hypocalcaemia is characterised by paraesthesia and muscle spasms
• Symptoms of hypocalcaemia (This usually occurs at calcium concentrations < 1.9 mmol/L):

  • Paraesthesia
  • Muscle cramps
  • Wheezing
  • Voice changes - laryngospasm
  • CNS disturbance - seizures, irritability and confusion
  • Chest pain
  • Palpitations - arrhythmias
• Hypocalcaemia can cause prolonged QT interval and arrhythmias
• Two clinical signs associated with hypocalcaemia:

  • Trousseau's sign: development of carpopedal spasm following inflation of a blood pressure cuff above systolic BP
  • Chvostek's sign: tapping over the course of the facial nerve in the pre-auricular area causes muscle spasms
• It is important to distinguish whether the cause of hypocalcaemia is acute or chronic. Acute severe hypocalcaemia (< 1.9 mmol) is a medical emergency that requires urgent treatment and cardiac monitoring.
• Usual investigations to determine the underlying cause:

  • Bone profile
  • U&Es
  • Vitamin D
  • Parathyroid hormone
  • Magnesium
• Management of acute hypocalcaemia:

  • IV calcium gluconate
  • Cardiac monitoring
• Management of chronic hypocalcaemia:

  • Oral calcium and vitamin D supplements e.g Adcal D3
• Transient hypoglycaemia can be treated with adcal
• Mild hypocalcaemia = above 1.9 or asymptomatic

  Severe = lower than 1.9 or symptomatic
• Hypoglycaemia can cause tetany - uncontrollable muscle spasms and rigidity
• Doses of vitamin D treatment:

  • Primary prevention - 400 units daily
  • Loading dose - 50000 units once weekly for 6 weeks
  • Maintenance - 800-2000 units daily
• Around 40% of calcium is bound to albumin in the bloodstream, and in this form, it is physiologically inactive. The remaining 60% is known as ionised or ‘free’ calcium, which is physiologically active.