Hypocalcaemia

CAUSES

• Most common causes
  • Hypoalbuminemia
  • Vitamin D Deficiency

• Intake reduced:
  • Ca2+
  • Vitamin D deficiency
  • phenytoin (increased metabolism of vitamin D)

• Redistribution:
  • alkalosis
  • citrate toxicity
  • hyperphosphataemia
  • pancreatitis
  • tumour lysis syndrome
  • rhabdomyolysis
  • decreased bone turnover
  • hypoparathyroidism
  • drugs (bisphosphonates, PPI’s, SSRI’s, gentamicin)

• Low Parathyroid Hormone (or normal Parathyroid Hormone level)
  • Hypomagnesemia
  • Hypoparathyroidism
    • Anterior neck surgery (75% of Hypoparathyroidism cases) – Thyroidectomy with operative Parathyroid removal (most common cause)- need : Post-surgical monitoring includes Serum Calcium and PTH levels
    • Hemochromatosis
    • Adrenal, Ovarian and Parathyroid failure
• High Parathyroid Hormone (secondary Hyperparathyroidism as a reflex response to Hypocalcemia)
  • Medication-Induced Hypocalcemia
  • Pancreatitis
  • Vitamin D Deficiency (Decreased 25-hydroxyvitamin D)

HISTORY

• perioral numbness
• paresthesias
• muscle cramps
• mild mental status changes (irritability)
• seizures
• tetany
• collapse
• to find cause: diet, drugs, symptoms specific to cause
• laryngospasm

EXAMINATION

• Chvostek sign (tapping facial nerve anterior to ear -> spasm of facial muscles)
• Trousseau sign (inflate BP cuff -> trap median nerve -> carpal spasm) 
• hypotension 
• arrhythmias (long QT)
• heart failure
• signs specific to cause

INVESTIGATIONS

• Albumin
• Calcium (corrected)
• Phosphate.
• Calcium (ionised)
  • if indicated.
  • Hypocalcaemia is only significant clinically if ionised calcium is reduced.
• PTH
• ECG: prolongation of ST segment and QT interval -> VT
• albumin
• lipase (rule out pancreatitis)
• U+E – renal failure, hyperkalaemia
• CK and urate – rhabdomyolysis

MANAGEMENT

• treat cause
• proportional to severity
• oral Ca2+
• replace Mg2+
• vitamin D
• if vitamin D deficient
  • commence oral vitamin D supplementation: load with colecalciferol 300,000units over 6-10 weeks e.g. 50,000units weekly for 6 weeks followed by a maintenance dose of 800-1000units daily.
• If patient has hypomagnesaemia
  • stop any precipitating drug and administer IV magnesium
• If post-thyroidectomy, repeat serum calcium 24 hours later. Then if:
  • Serum adjusted calcium >2.2mmol/L, patient may be discharged with plan to re-check serum calcium within one week.
  • Serum adjusted calcium remains between 1.9-2.2mmol/L, increase Calcichew Forte Chewable to three tablets twice a day (unlicensed dose)*.
  • Patient remains in mild hypocalcaemic range 72 hours post-operatively despite calcium supplementation, start alfacalcidol oral 0.25microgram daily. Alfacalcidol is restricted to specialist initiation; contact a senior member of medical staff to discuss use.
• IV calcium (10mL gluconate = 2.3mmol = 93mg, 10mL chloride = 6.8mmol = 272mg)
• indications for IV calcium therapy:
  • symptomatic hypocalcaemia
  • ionized Ca2+ <0.8mmol/L
  • hyperkalaemia
  • Ca2+ channel blocker OD
  • hypermagnesaemia
  • hypocalcaemia with high inotrope requirement
  • massive transfusion
  • post cardiopulmonary bypass