Overview
Hypocalcaemia
Topic Overview
Summary
Hypocalcaemia is serum corrected calcium under 2.1 mmol/L (or ionised calcium under 1.0 mmol/L). It causes neuromuscular excitability (tetany, paraesthesia, Chvostek's and Trousseau's signs), cardiac complications (QT prolongation, arrhythmias), and seizures. Common causes are hypoparathyroidism (post-surgical), vitamin D deficiency, and chronic kidney disease. Severe symptomatic hypocalcaemia requires IV calcium gluconate. Always check and correct magnesium.
Key Facts
- Definition: Corrected Ca under 2.1 mmol/L (or ionised Ca under 1.0 mmol/L)
- Symptoms: Tetany, paraesthesia (perioral, fingers), muscle cramps
- Signs: Chvostek's sign, Trousseau's sign
- ECG: QT prolongation
- Treatment: IV calcium gluconate (10 mL 10%, slow); correct magnesium
- Chronic: Oral calcium + vitamin D supplements
Clinical Pearls
Always correct calcium for albumin: Corrected Ca = measured Ca + 0.02 × (40 − albumin)
Post-thyroidectomy hypocalcaemia = hypoparathyroidism until proven otherwise
Hypocalcaemia + hypomagnesaemia = refractory until magnesium corrected
Why This Matters Clinically
Severe hypocalcaemia causes life-threatening tetany, laryngospasm, and cardiac arrhythmias. Prompt recognition and IV calcium replacement is life-saving.
Visual Summary
Visual assets to be added:
- Chvostek's and Trousseau's signs demonstration
- ECG showing prolonged QT
- Calcium homeostasis diagram
- Hypocalcaemia management algorithm
Epidemiology
Incidence
- Common in hospitalised patients
- Particularly post-surgical (thyroidectomy, parathyroidectomy)
- Common in CKD and elderly
Demographics
- All ages
- Higher in elderly (vitamin D deficiency)
- Higher in CKD patients
Causes
| Category | Examples |
|---|---|
| Hypoparathyroidism | Post-surgical (most common), autoimmune, infiltrative |
| Vitamin D deficiency | Dietary, malabsorption, lack of sunlight |
| Chronic kidney disease | Reduced 1,25(OH)2D production |
| Acute pancreatitis | Calcium sequestration |
| Hypomagnesaemia | Impairs PTH secretion and action |
| Drugs | Bisphosphonates, denosumab, cinacalcet |
| Massive transfusion | Citrate binds calcium |
| Hungry bone syndrome | Post-parathyroidectomy |
Pathophysiology
Calcium Homeostasis
- Normal total calcium: 2.1-2.6 mmol/L
- Ionised (free) calcium: ~50% of total
- Remainder bound to albumin and anions
- Regulated by PTH, vitamin D, calcitonin
Effects of Low Calcium
| System | Effect |
|---|---|
| Neuromuscular | Increased excitability → tetany, paraesthesia |
| Cardiac | QT prolongation, arrhythmias |
| CNS | Seizures, altered mental status |
Why Alkalosis Worsens Symptoms
- Alkalosis increases calcium binding to albumin
- Reduces ionised calcium
- Exacerbates symptoms at same total calcium
Why Magnesium Matters
- Hypomagnesaemia impairs PTH secretion
- Also impairs PTH action on target tissues
- Hypocalcaemia is refractory until Mg corrected
Clinical Presentation
Symptoms
Signs
Red Flags
| Finding | Significance |
|---|---|
| Tetany | Severe — needs IV calcium |
| Laryngospasm | Airway emergency |
| Seizures | Severe hypocalcaemia |
| QT prolongation | Arrhythmia risk |
| Post-thyroidectomy | Hypoparathyroidism |
Perioral paraesthesia
Common presentation.
Finger/toe paraesthesia
Common presentation.
Muscle cramps
Common presentation.
Muscle stiffness
Common presentation.
Anxiety, confusion
Common presentation.
Clinical Examination
Neurological
- Chvostek's sign (tap facial nerve anterior to ear)
- Trousseau's sign (inflate BP cuff above systolic for 3 minutes → carpopedal spasm)
- Hyperreflexia
- Tetany
Cardiovascular
- Signs of heart failure (if severe)
General
- Signs of underlying cause (surgical scar, rickets features)
Investigations
Blood Tests
| Test | Purpose |
|---|---|
| Serum calcium | Confirm hypocalcaemia |
| Albumin | Calculate corrected calcium |
| Ionised calcium | More accurate (if available) |
| Phosphate | High in hypoparathyroidism, CKD |
| Magnesium | Correct if low |
| PTH | Low = hypoparathyroidism; high = secondary cause |
| Vitamin D (25-OH) | Deficiency |
| U&E, creatinine | CKD |
Corrected Calcium Formula
Corrected Ca = measured Ca + 0.02 × (40 − albumin)
ECG
- QT prolongation
- May see arrhythmias
Classification & Staging
By Severity
| Severity | Calcium Level | Features |
|---|---|---|
| Mild | 1.9-2.1 mmol/L | Often asymptomatic |
| Moderate | 1.5-1.9 mmol/L | Paraesthesia, cramps |
| Severe | Under 1.5 mmol/L | Tetany, seizures, arrhythmia |
By Cause
- Hypoparathyroidism (PTH low)
- Vitamin D deficiency (PTH high, 25-OH vit D low)
- CKD (PTH high, phosphate high)
Management
Severe/Symptomatic Hypocalcaemia — Emergency
1. IV Calcium Gluconate:
- 10 mL of 10% calcium gluconate (2.25 mmol) IV over 10 minutes
- Cardiac monitoring
- Repeat if needed
- May need continuous infusion (100 mL 10% in 1L 5% dextrose over 24h)
2. Check and Replace Magnesium:
- IV magnesium sulphate if low
- Hypocalcaemia is refractory if magnesium not corrected
3. Treat Underlying Cause
Mild/Chronic Hypocalcaemia
| Treatment | Details |
|---|---|
| Oral calcium | Calcium carbonate or citrate 1-2g/day in divided doses |
| Vitamin D | Cholecalciferol (vitamin D3) or calcitriol (active form) |
| Monitor | Regular calcium levels |
Post-Thyroidectomy / Hypoparathyroidism
- Alfacalcidol or calcitriol (active vitamin D)
- Oral calcium supplements
- Monitor for hypercalcaemia
CKD-Related
- Phosphate binders
- Alfacalcidol
- Treat secondary hyperparathyroidism
Complications
Of Hypocalcaemia
- Tetany
- Laryngospasm (airway emergency)
- Seizures
- Cardiac arrhythmias (torsades de pointes)
- Cataracts (chronic)
- Basal ganglia calcification (chronic hypoparathyroidism)
Of Treatment
- Hypercalcaemia (over-treatment)
- Extravasation injury (IV calcium)
Prognosis & Outcomes
Prognosis
- Excellent with prompt treatment
- Severe symptomatic hypocalcaemia can be fatal if untreated
Long-Term
- Chronic hypoparathyroidism requires lifelong treatment
- Regular monitoring essential
Evidence & Guidelines
Key Guidelines
- Endocrine Society Clinical Practice Guideline on Hypoparathyroidism
- NICE CKD Guidelines (calcium/phosphate management)
Key Evidence
- IV calcium gluconate is safe and effective
- Magnesium correction essential for refractory hypocalcaemia
Patient & Family Information
What is Hypocalcaemia?
Hypocalcaemia means low calcium levels in your blood. Calcium is important for your muscles, nerves, and heart.
Causes
- Thyroid or parathyroid surgery
- Low vitamin D
- Kidney problems
Symptoms
- Tingling around the mouth or fingers
- Muscle cramps or spasms
- Feeling anxious or confused
Treatment
- Calcium through a drip (if urgent)
- Calcium tablets and vitamin D supplements
Resources
References
Primary Guidelines
- Brandi ML, et al. Management of Hypoparathyroidism: Summary Statement and Guidelines. J Clin Endocrinol Metab. 2016;101(6):2273-2283. PMID: 26943721
Key Reviews
- Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. BMJ. 2008;336(7656):1298-1302. PMID: 18535071
- Shoback D. Hypoparathyroidism. N Engl J Med. 2008;359(4):391-403. PMID: 18650515