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

Clinical

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

Complication

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

Correction

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

Asymptomatic

• Oral Calcium supplements and Vitamin D rich milk

Symptomatic

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

References and Links

• CCC – Calcium metabolism
• CCC – Calcium basics
• CCC – Hypercalcaemia Overview
• CCC – Hypocalcaemia
• CCC – Calcium replacement (advantages/disadvantages)
• CCC – Calcium as an inopressor

CCC Differential Diagnosis Series
NEURO	Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision
RESP	Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement
CVS	Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction
GIT	Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage
GUT	Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency,
MSK	Arthritis, Shoulder pain, Wasting of the small muscles of the hand
DERM	Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans
ENDO	Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss
HAEM	Splenomegaly
PAEDS	Floppy infant
MISC	Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest
IMAGING	CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR, ABDO: Gas on abdominal X-ray, Kidney mass, BRAIN: Intracranial calcification, Intracranial structures with contrast, Ventriculomegaly, OTHER: Pseudofracture on X-Ray,
LABS	LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia,  HIGH: Bilirubin and Jaundice, Hyperammonaemia, Hypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia,  ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis, Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes

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