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Dietary sources of calcium
Dietary sources of calcium include milk and other dairy products, notes and seeds, fish, dates broccoli and other leafy green vegetables.

Roles of Calcium

  • Contraction of skeletal, cardiac and smooth muscle
  • Blood clotting
  • Control of nerve impulses
    • Increases in the level of calcium cause depression of the nervous system
    • Decreases in the level of calcium causes excitation of the nervous system
Levels of calcium are controlled by PTH. PTH causes:
  • Increased osteoclast activity
  • Decreased excretion of calcium by the kidneys


Hypocalcaemia is sometimes artificially seen in hypoalbuminaemia, because about 40% of calcium travels in the blood bound to albumin

Signs & Symptoms

  • Tetanythis most commonly occurs in the hands first, with flexed wrist and fingers together, where it is called carpo-pedal spasm.
    • Is some cases, this can be elicited by occluding the brachial artery (e.g. with blood pressure cuff). This is Trousseau’s sign
  • Seizures – due to increased excitability of neurons.
  • Increased contractility and increased neuron activity
  • Peri-oral parasthesia
  • Neuromuscular excitability – Chvostek’s sign – tapping over the facial nerve causes facial muscle to twitch
  • Cataractsin chronic hypocalcaemia


  • Renal Failure
  • PTH deficiency (hypoparathyroidism, e.g. after thyroid surgery, where the parathyroid glands have been removed) – note that is also may be associated with hyperparathyroidism when the low Ca2+ is causing the hyperparathyroidism (secondary hyperparathyroidism)
  • Insufficient vitamin D
  • Insufficient calcium in diet (rare)
  • Excess magnesium in diet (rare)


Signs & Symptoms

  •  “Bones, stones, groans and psychic moans”
  • Depressed nervous system – this can lead to slow reflexes.
  • Poly uria / polydipsia
  • Decreased QT interval
  • Lack of appetite and constipation and vomiting – probably due to decreased contractility of the muscle walls of the GIt.
  • Decreased contractility and decreased neuron activity
  • Formation of calcium phosphate crystals at very high levels of Ca2+ in the blood
  • Decreased QT interval on ECG


Primary and tertiary hyperparathyroidism (PTH excess)
Bone metastases – These causes can be differentiated by looking at:

  • albumin
  • ↓ chloride
  • ↓ potassium
  • Alkylosis
  • If these three factors are present, then the cause is likely metastatic

Dehydration – may seem very obvious I know, but you should check the level of urea – as if urea is high, then dehydration (or renal failure!) is likely.
Rare causes:


  • Saline 0.9% IV
  • Correct any hypokalaemia and hypomagnesia. This will reduce symptoms and increase renal excretion of calcium
  • Bisphosphonate – e.g. pamidronate – these reduce osteoclast activity. Give a single dose. Will lower blood calcium over 2-3day period
  • Diuretics may be considered (e.g. Frusemide). Thiazide diuretics should not be used.

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

This Post Has 2 Comments

  1. fergus

    you said if urea is low dehydration is lkely- whereas it should if urea is high dehydration is likely 🙂

  2. sarah

    My understanding is low not high magnesium from eg Gi loss or renal loss of certain drugs eg diuretics/alcohol inhibits PTH and hence cause low calcium.

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