Hypocalcemia

Background

Serum Levels

Normal value ranges may vary among different laboratories (see examples below)

• Harbor-UCLA low: <8.9 (Ionized: <2.0 ionized)
  • UCSF low: <4.8 mg/dL or <1.20 millimol/L
• Critical low: <6.6 (<1.5 ionized)

• Correct for hypoalbumimia
  • Corrected Ca = (0.8 *(Normal Alb - Patient's Alb)) + Serum Ca

Fraction

• 15% bound to anions (phosphate, lactate, citrate)
• 40% bound to albumin
• 45% free (regulated by PTH, Vit-D)

Causes

• Misc
  • Shock
  • Sepsis
  • Pancreatitis
  • Hypomag
  • Rhabdo (phosphate overload)
  • Massive transfusion
  • Systemic Hydrofluoric Acid toxicity
  • DiGeorge syndrome
• Decreased absorption
  • Vitamin D deficiency
• Increased excretion
  • Alcoholism
  • Renal Failure
  • Diuretics
• Endocrine
  • Hypoparathyroidism
• Drugs
  • Cimetidine
  • Phenytoin
  • Lasix, loop diuretics
  • Norepinephrine
  • Glucagon
  • Glucocorticoids
  • Magnesium sulfate
  • Nitroprusside

Clinical Features

• Paresthesias (mouth, fingertips)
• ↑ DTRs
• Cramps
• Weakness
• Confusion
• Seizures
• Chvostek/Trousseau signs, Tetany
• Hallucinations
• Laryngospasm
• Bronchospasm
• Cardiac dysrhythmias

Differential Diagnosis

Jaw Spasms

• Acute tetanus
• Akathisia
• Conversion disorder
• Drug toxicity (anticholinergic, phenytoin, valproate, carbamazepine)
• Dystonic reaction
• Electrolyte abnormality
  • Hypocalcemic tetany
  • Magnesium
• Mandible dislocation
• Meningitis
• Peritonsillar abscess
• Rabies
• Seizure
• Strychnine poisoning
• Stroke
• Temporomandibular disorder
• Torticollis

Evaluation

ECG

Hypocalcemia with QTc prolongation

• QT Prolongation via increasing the ST length
  • Only hypothermia and hypocalcemia prolong QT this way

Trousseau's Sign (Mod to high SN and SP)

Spasm associated with symptomatic hypocalcemia

• Inflate BP cuff for 2-3 mins
• Positive = Muscle contractions of the hand and wrist

Chvostek's Sign (Low SN and SP)

• Tapping on the face just anterior to the ear and just below the zygomatic bone
• Positive = Ipsilateral facial twitching

Labs

• BMP
• Mag, Phos
• PTH (secondary hyperparathyroidism)

Management

Avoid empiric treatment in patients taking digoxin due to risk for Stone Heart

• Asymptomatic
  • Calcium gluconate 1 gm PO Q6hrs
  • Vitamin D (calcitriol) 0.2 mcg BID
• Symptomatic
  • Calcium gluconate/chloride 10mL of 10% soln IV over 10min
• Correct hypomag at same time (otherwise PTH is inhibited)
• Avoid phenothiazine antipsychotics (may precipitate extrapyramidal symptoms)
• Avoid furosemide (may worsen hypocalcemia)

Disposition

• Admit all symptomatic patients

See Also

• Electrolyte Abnormalities (Main)

Video

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