Serum Levels

Normal value ranges may vary slightly among different laboratories

  • Low: <8.9 mg/dL[1] (Ionized: <4.8 mg/dL or <1.20 millimol/L[2])
  • Critical low: <6.6 mg/dL[3] (Ionized: <3.5 mg/dL[4])

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


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


Clinical Features

Symptoms of hypocalcemia

Differential Diagnosis

Movement Disorders and Other Abnormal Contractions

Jaw Spasms



Hypocalcemia with QTc prolongation
  • QT Prolongation via increasing the ST length
    • Only hypothermia and hypocalcemia prolong QT this way

Trousseau's sign

Spasm associated with symptomatic hypocalcemia
  • Inflate BP cuff for 2-3 minutes
  • Positive = Muscle contractions of the hand and wrist
  • Specificity 99%, sensitivity 94%

Chvostek sign

  • Tapping on the face just anterior to the ear and just below the zygomatic bone
  • Positive = Ipsilateral facial twitching
  • Specificity 96%, sensitivity 26%


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


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


  • Admit all symptomatic patients

See Also


  1. Harbor-UCLA computer system accessed 08/15/2019
  2. https://www.ucsfhealth.org/tests/003486.html
  3. Harbor-UCLA computer system accessed 08/15/2019
  4. http://www.clinlabnavigator.com/calcium-ionized.html
  5. Yu, AS. Relation between total and ionized serum calcium concentrations. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA. (Accessed on October 6th, 2016.)