Hypocalcemia

Table of Contents

Calcium Metabolism
Dietary Metabolism
Skeletal Metabolism
Renal Metabolism
Differential Diagnosis
Clinical Presentation
Symptoms
Signs
Lab Values
Normal Ranges
Management
Acute Treatment
Chronic Treatment
References

Calcium metabolism

Dietary metabolism

  • Calcium is absorbed in the gut under the influence of activated vitamin D.
    • PTH (parathyroid hormone) increases the renal secretion of activated vitamin D.
    • Activated vitamin D binds to VDR (vitamin D receptor) in the gut to increase calcium absorption

Skeletal metabolism

  • 99% of total body calcium is stored as a calcium-phosphate complex in the bone
  • PTH increases osteosclastic activity, resulting in bone resorption and release of calcium into the circulation
  • Calcitonin decreases osteoclastic activity
    • Calcitonin is produced by parafollicular cells in the thyroid (also known as C cells).
    • Calcitonin may be elevated in medullary thyroid cancer (which originates from C cells)

Renal Metabolism

  • PTH increases calcium reabsorption and decreases phosphate reabsorption in the renal rubules
    • This increases the calcium to phosphate ratio in the blood

Differential

  • Renal failure (reduced synthesis of vitamin D and impaired calcium reabsorption)
  • Vitamin D deficiency (reduced intestinal absorption of calcium)
  • Hypoparathyroidsm (reduced osteoclastic activity, increased renal excretion of calcium, increased renal reabsorption of phosphate)
  • Hyperphosphatemia (calcium binds to phosphate in the blood and becomes an insoluble, inactive complex)

Presentation

Symptoms

  • Peri-oral numbness
  • Paresthesia in finger tips
  • Spasms/tetany
  • Confusion/decreased LOC

Signs

  • Chvostek’s sign: tapping over the facial nerve results in facial spasm
  • Trousseau’s sign: inflate a blood pressure cuff over the biceps (at a pressure greater than the systolic BP) for 3 minutes. Carpal spasm (flexion) during this test is a sign of hypocalcemia.
  • ECG changes: prolonged QT interval, arrythmias

Lab values

Normal ranges

  • Ionized calcium: 1.1–1.3 mmol/L
  • Phosphate: 0.81–1.47 mmol/L
  • PTH: 1.2–5.7 pmol/L

Management

Acute treatment

  • IV calcium bolus over 10–15 minutes
    • Rapid infusion can lead to arrythmias
  • Close monitoring (telemetry recommended)
  • Serial bloodwork (serum calcium and albumin or ionized calcium)

Chronic treatment

  • Oral calcium and vitamin D supplementation
    • Elemental calcium: 1.5–2 g divided TID
    • Vitamin D
      • Example: calcitriol (Rocaltrol): initial dosing 0.25 mcg/day

References

  1. Goldenberg, D., Goldstein, BJ. Handbook of Otolaryngology Head and Neck Surgery. Section 5.4.12: Calcium Disorders.
  2. Lexicomp. Calcitriol: Drug Information.
  3. Peacock M. Calcium metabolism in health and disease. Clin J Am Soc Nephrol. 2010 Jan;5 Suppl 1:S23–30.

Section Author

Scott Kohlert
Medical Student (MS-4)
University of Ottawa

Section Editor

This section has not yet been peer reviewed.