Hypocalcemia

Epidemiology

---

Etiology

---

Pathophysiology

---

Clinical features

---

Neurological manifestations

• Tetany: increased neuromuscular excitability (when caused by respiratory alkalosis = hyperventilation-induced tetany)
  • Paresthesias: typically tingling or pins-and-needles sensation in extremities and/or in the perioral area
  • Spasms (e.g., carpopedal spasm, bronchospasm or laryngospasm), and cramps (possible in any muscle)
  • Stiffness, myalgia
  • Maneuvers to elicit latent tetany on physical exam
    • Chvostek sign: short contractions (twitching) of the facial muscles elicited by tapping the facial nerve below and in front of the ear (∼ 2 cm ventral to the ear lobe)
    • Trousseau sign: ipsilateral carpopedal spasm occurring several minutes after inflation of a blood pressure cuff to pressures above the systolic blood pressure
• Seizure: may be the initial or only symptom

Diagnostics

---

• Initial/Screening: Serum ionized calcium (physiologically active form) or Corrected total calcium for hypoalbuminemia.
  • Formula: Corrected Ca = measured Ca + 0.8 * (4.0 - albumin). c
  • If serum albumin drops (e.g., NS, cirrhosis, malnutrition), the protein-bound fraction of ${\text{Ca}}^{2+}$ decreases, which drops the measured total serum ${\text{Ca}}^{2+}$.
  • Biochemical studies demonstrate that for every $1.0\text{ g/dL}$ drop in serum albumin below the normal baseline, the total serum ${\text{Ca}}^{2+}$ concentration decreases by approximately $0.8\text{ mg/dL}$.
  • $4.0\text{ g/dL}$ is used as the standard reference value for “normal” serum albumin.
• Acute Symptomatic/Severe Hypocalcemia (tetany, seizures, arrhythmias):
  • IV calcium gluconate is preferred (less risk of tissue necrosis than CaCl2 if extravasated).
  • Correct concurrent hypomagnesemia if present.
• Chronic/Asymptomatic Hypocalcemia:
  • Oral calcium (carbonate or citrate) and vitamin D supplements (e.g., calcitriol in CKD or hypoparathyroidism).
  • For hypoparathyroidism, may add thiazide diuretics to decrease urinary Ca2+ excretion.

Treatment

---