Hypocalcaemia DDx

Causes of HYPOcalcaemia

Commonest causes: HYPOalbuminaemia and HYPERventilation

  1. Factitious (commonest)
    • Low albumin
  2. Metabolic (transcellular as for potassium)
    • Primary respiratory alkalosis (HYPERventilation)
    • Chronic alkalosis
  3. Endocrine (Decreased Ca uptake, increased excretion)
    • Reduced PTH (associated raised PO4 as cannot excrete)
      • Hypoparathyroidism (raised PO4)
      • Pseudohypoparathyroidism (raised PO4)
      • Thyroid or parathyroid surgery
    • Increased calcitonin (decreased Ca and PO4)
      • Medullary thyroid carcinoma
    • Decreased Vitamin D (decreased GIT calcium absorption (small))
  4. Increased PHOSPHATE(precipitates calcium in serum)
    • Tumour lysis syndrome (↑K+ ,↑PO4, ↓Ca++)
    • Rhabdomyolysis
    • Chronic renal failure
  5. Excessive CITRATE in circulation (precipitates calcium)
    • Whole blood transfusion
    • Plasmapheresis
  6. Increased bone formation and turnover (Osteoblastic activity)
    • Malignancy (Breast, lung, thyroid, kidney, prostate)
    • Osteomalacia (Increased alkaline phosphatase)
  7. Other
    • Sepsis and Toxic shock syndrome
    • Pancreatitis (PO4 normal)
    • Overhydration
  8. Drugs
    • B blocker OD, phenytoin, gentamicin, heparin
    • Cimetidine, Ca channel blocker


Calcium is excitable membrane stabiliser. Neuromuscular excitability and irritability is predominant

  • Neurological
    • Hyperreflexia and seizures
    • Paraesthesia of extremities and face (Digital and peri-oral)
    • Confusion, hallucinations, dementia
  • Muscular
    • Laryngospasm, stridor, tetany
    • Muscle spasm, cramps and tetany
      • Chvostek sign (Facial nerve tap….twitch corner of mouth)
      • Trousseau sign (BP cuff on arm for 3mins induces carpopedal spasm)
  • Cardiac
    • Decreased myocardial contractility and heart failure


  • Arrhythmia
  • ECG changes
  • QTc prolongation (With low K+, Mg2+, Ca2+)
  • T wave inversion
  • Complete heart block
  • Torsades des Pointes


  • Assess and treat underlying cause
  • Correct acidosis and hypomagnesaemia
  • Replace Calcium


  • Oral Calcium supplements and Vitamin D rich milk


  • Parenteral Calcium
    • Calcium chloride (10ml 10% 13.6mEq)
    • Calcium gluconate (10ml 10% 4.6mEq)

References and Links

CCC 700 6

Critical Care


Associate Professor Curtin Medical School, Curtin University. Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM Sir Charles Gairdner Hospital.  Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.