See also:

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

  • Tetany – this 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
  • Cataracts –in 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 as with all ions, you should check the level of urea – as if urea is also low, then dehydration is likely.
Rare causes: