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Electrolyte Abnormalities




Hypocalcaemia, or a reduced serum calcium concentration >2.15 mmol/L, prolongs action potentials which primarily results in delayed ventricular repolarisation (prolonged QT) on ECG.


  • Causes of Hypocalcaemia

  • Hypoparathyroidism - iatrogenic, autoimmune, congenital
  • PTH resistance - pseudohypoparathyroidism, hypomagnesaemia
  • Vitamin D deficiency - inadequate intake, low sun exposure, malabsorption, liver failure, chronic kidney disease
  • Increased excretion / reduced bony turnover - loop diuretics, osteoporosis, cachexia, bisphosphonates, malignancy
  • Extravascular calcium buildup - osteoblastic metastases, sepsis, pancreatitis
  • Calcium chelation - alkalosis, citrate, EDTA, hyperphosphataemia
  • Genetic - familial hypoparathyroidism, DiGeorge syndrome


  • Clinical Features

  • Hyperreflexia
  • Tetany (Chvostek’s & Trousseau’s signs)
  • Seizures
  • Heart failure (due to reduced  contractility)


  • Bloods

  • Total calcium <2.15 mmol/L
  • Ionised calcium < 1.15 mmol/L
  • ECG Findings

  • Prolonged QT interval (due to a prolonged ST segment)
  • Torsade de pointes (rare)
  • Diagnosis
  • Further Investigations

  • Check the patient's PTH, phosphate, vitamin D and magnesium levels. If a cause is not evident and hypocalcaemia is ongoing (i.e. not lab error) then further investigation may be warranted.
  • Diagnosis
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