creation date: 2026-08-24 18:35
tags: Pathologies
Hypocalcemia
Background
Definitions
Hypocalcemia is an abnormally low serum calcium level.
Most calcium within the body is found in the bones as calcium phosphate. In the serum:
- 45% is bound to protein (albumin)
- 45% is active form as free or ionized calcium
- 10% is bound to anions
Normal range is 2.1-2.5 mmol/L.
Etiology & Pathophysiology
Calcium is regulated with PTH and vitamin D. Calcium levels are detected via a calcium-sensing receptor (CaSR) which controls PTH secretion. PTH is secreted in response to reduction in ionized calcium and thus increases calcium within the serum. Vitamin D, in its active form 1,25-dihydroxyvitamin D (calcitriol), is used in the absorption from the GI tract.
Hypocalcemia is broadly due to 3 categories.
Parathyroid hormone deficiency
- Destruction of parathyroid glands (eg. surgical, autoimmune, irradiation, infiltrative diseases)
- Abnormal parathyroid gland development (genetics)
- Altered PTH regulation (eg. mutation for preproPTH, mutations of CaSR pathway)
High parathyroid hormone levels
- Vitamin D deficiency/resistance (poor intake, malabsorption)
- Chronic kidney disease (causes decrease in calcitriol)
- Pseudohypoparathyroidism (PTH resistance) – heterogenous disorders of specific organs not responding to PTH due to postreceptor signally pathway alteration
- Extravascular deposition
- Hyperphosphatemia or excess tissue breakdown – deposition in bone primarily
- Osteoblastic metastases – deposition in bone around tumour
- Acute pancreatitis – precipitation of calcium soaps in abdominal cavity
- Sepsis or severe illness
- Surgery – citrate use as anticoagulant chelates calcium
**Pharmacological/drugs
- Calcium chelators (citrate, lactate, foscarnet, EDTA)
- Bisphosphonates (especially when used when vitamin D deficiency)
- Denosumab
- Cinacalcet
- Immune checkpoint inhibitors
- Chemotherapy
- Excess fluoride
Risk Factors
Clinical Presentation
Signs & Symptoms
The hallmark finding is tetany – neuromuscular irritability/hyperexcitability of neurons
- Mild: perioral numbness, paresthesias of hand/feet, muscle cramps
- Severe: carpopedal spasm, laryngospasm, focal/generalized seizures
- Non-specific: fatigue, hyperirritability, anxiety, depression
- Trousseau’s sign (induction of carpal spasm by infation of sphygomomanometer above SBP for 3 minutes)
- Chvostek’s sign (contraction of ipsilateral facial muscle by tapping the facial nerve just anterior of the ear)
Other findings include:
- Seizures
- Cardiovascular (hypotension, myocardial dysfunction)
- Papilledema
- Psychiatric manifestations
Additional findings may be present depending on the etiology:
Hypoparathyroidism:
- Basal ganglia calcifications
- Cataracts
- Dental abnormalities
- Ectodermal manifestations
Pseudohypoparathyroidism:
- Hypocalcium, hyperphosphatemia, hyper-PTH
- Variants of PHP have skeletal abnormalities, intellectual impairment, resistance to hormones etc.
Vitamin D deficiency:
- Rickets and osteomalacia
- Muscle weakness and hypotonia
- Motor retardation
- Stunted growth
History & Physical Exam
History should include:
- Family history
- History of surgery, especially around the neck
- History of autoimmune disease
- Medication and drug review
Physical exams can include Chvostek’s and Trousseau’s which are strongly suggestive of hypocalcemia.
Diagnosis
Criteria
Diagnosis of hypocalcemia is made with a serum calcium concentration.
Ionized calcium is ideal and more accurate as even corrected total calcium may be inaccurate in some populations (eg. CKD).
Work-up
Verification of hypocalcemia
For decreased calcium levels, confirmation should be done by correcting based on albumin.
- Hypoalbuminemia can falsely lower serum calcium levels
- Hyperalbuminemia can underestimate the severity
Ionized calcium levels can also be used if available and is the gold standard.
Laboratory studies
In all patients:
- Serum parathyroid hormone
- Albumin to correct calcium
Additional evaluation may be done to determine etiology:
- Serum magnesium
- Creatinine
- Phosphate
- Vitamin D metabolites (calcidiol and calcitriol)
- ALP
- amylase
- Urinary calcium and magnesium
Differential
Red Flags / Complications
Management
Severely Symptomatic / Acute Hypocalcemia
For patients with any of the following:
- Symptoms (eg. carpopedal spasm, laryngospasm, bronchospasm, seizures)
- Prolonged QT interval
- Asymptomatic but acute decrease in corrected calcium to ≤1.9 mmol/L
Treatment consist of IV calcium:
- 1-2 g of calcium gluconate (equivalent to 90-180 mg elemental Ca)
- In 50 mL of 5% dextrose or normal saline
- Infused over 10-20 minutes
- Repeat after 10-60 minutes as needed to resolve symptoms
followed by a slow infusion of calcium with persistent hypocalcemia.
- 10% calcium gluconate
- Administered at 50 mL/hour, adjusted to maintain the serum calcium concentration at the lower end of the normal range
In patients with concurrent hypomagnesemia, magnesium will likely need to be corrected first as hypomagnesemia induces resistance to PTH and reduces secretion, making hypocalemia hard to correct.
- 2 g magnesium sulfate infused as a 10% solution over 10-20 minutes
- 1 g magnesium sulfate in 100 mL of fluid per hour
- Continue until serum magnesium ≥0.4 mmol/L
More oral supplementation may be necessary for persistent hypomagnesemia (eg. those with malabsorption).
Mildly Symptomatic / Chronic Hypocalcemia
For patients with milder acute hypocalcemia (corrected calcium >1.9 mmol/L) or chronic hypocalcemia treat with oral 1-2 g elemental calcium given as calcium carbonate or calcium citrate daily in divided doses.
This is typically given as calcium carbonate (40% elemental) or calcium citrate but other options are available and elemental calcium concentration are typically listed.
In cases where oral calcium does not work (unable to absorb, poor response), IV calcium is indicated.
Long Term Management
In specific cases, chronic management may be necessary.
Hypoparathyroidism
In cases where PTH is low, administration of calcium alone is often only transiently effective. Long term management requires:
- Lifelong calcium
- Vitamin D supplementation
Vitamin D deficiency
Hypocalcemia due to vitamin D deficiency is treated with either:
- Ergocalciferol (vitamin D2)
- Cholecalciferol (vitamin D3)
If uncomplicated, vitamin D is supplemented with 50,000 IU weekly for 6-8 weeks.
Chronic kidney/liver disease
For CKD patients, asymptomatic patients are treated with oral calcium to bind intestinal phosphate to prevent bone disease.
For liver disease, vitamin D metabolites may be needed (as vitamin D metabolism may be abnormal).
- 25-hydroxyvitamin D
Drug-induced hypocalcemia
Correct predisposing factors that affect absorption. Vitamin D and calcium supplementation are likely required.