Hypocalcaemia
Serum adjusted calcium <2.1 mmol/L. Commonest causes are vitamin D deficiency and hypoparathyroidism (post-surgical). Presents with neuromuscular excitability — tetany, perioral paraesthesia, seizures. Severe hypocalcaemia with prolonged QT is a medical emergency requiring IV calcium gluconate.
Key Facts
Commonest causes: vitamin D deficiency (most common overall), hypoparathyroidism (post-surgical — most common acute cause), chronic kidney disease Clinical features: neuromuscular excitability — perioral/digital paraesthesia, carpopedal spasm, tetany, Chvostek sign, Trousseau sign, seizures, laryngospasm ECG: prolonged QT interval (risk of Torsades de Pointes) Acute treatment: symptomatic or Ca²⁺ <1.9 mmol/L → IV calcium gluconate 10% 10mL over 10 minutes (with cardiac monitoring) → infusion; check and replace magnesium (Mg²⁺ required for PTH action) Chronic treatment: vitamin D deficiency → cholecalciferol (loading + maintenance); hypoparathyroidism → alfacalcidol/calcitriol + oral calcium Always check: PTH (primary differentiator), phosphate (high → hypoparathyroidism/CKD; low → vitamin D deficiency), magnesium, vitamin D, ALP, renal function
Overview
Key Facts
The approach to hypocalcaemia is guided by PTH and phosphate levels. Vitamin D deficiency is extremely common in the UK (~20% of adults). Post-surgical hypocalcaemia is the commonest acute presentation. Always check magnesium.
Epidemiology
Vitamin D deficiency: ~20% of UK adults have 25-OH-D <25 nmol/L. Post-thyroidectomy hypocalcaemia: transient ~10-30%, permanent ~1-2%.
Aetiology
Low PTH (hypoparathyroidism): post-surgical, autoimmune, DiGeorge, hypomagnesaemia. High PTH (secondary HPT): vitamin D deficiency (commonest), CKD, malabsorption (coeliac, IBD), pseudohypoparathyroidism. Other: pancreatitis (Ca²⁺ saponification), rhabdomyolysis, massive blood transfusion (citrate chelates Ca²⁺), hyperphosphataemia (tumour lysis), alkalosis (increased protein binding → lower ionised Ca²⁺).
Pathophysiology
Calcium homeostasis: PTH, vitamin D, and calcitonin regulate serum calcium through bone resorption, renal reabsorption, and intestinal absorption. Deficiency of PTH or vitamin D → reduced calcium from all three sources. Low ionised calcium → increased neuronal excitability → tetany, seizures. Cardiac effects: prolonged QT interval.
Clinical Presentation
Acute
- Perioral paraesthesia: earliest symptom
- Digital paraesthesia: fingers, toes
- Muscle cramps, carpopedal spasm
- Tetany: sustained involuntary muscle contraction
- Laryngospasm: stridor — emergency
- Seizures: generalised tonic-clonic
- Chvostek sign: facial nerve tap → facial twitch
- Trousseau sign: BP cuff → carpopedal spasm (more specific)
Chronic
- Fatigue, depression, anxiety
- Dry skin, brittle nails, coarse hair
- Dental enamel hypoplasia
- Cataracts
- Basal ganglia calcification
- Osteomalacia (vitamin D deficiency — bone pain, proximal myopathy)
ECG
- Prolonged QT interval
Red Flags
- Post-surgical perioral tingling → urgent calcium check
- Laryngospasm/stridor → emergency
- Seizure with hypocalcaemia → IV calcium
- Prolonged QT → cardiac monitoring
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Vitamin D deficiency | HIGH PTH, LOW phosphate, raised ALP | 25-OH vitamin D |
| Hypoparathyroidism | LOW PTH, HIGH phosphate | PTH |
| CKD | HIGH PTH, HIGH phosphate, low eGFR | eGFR, PTH |
| Pseudohypoparathyroidism | HIGH PTH, Albright phenotype | PTH, genetic testing |
| Hypomagnesaemia | Impairs PTH function | Serum Mg²⁺ |
| Acute pancreatitis | Abdominal pain, raised amylase | Amylase, lipase |
Diagnosis / Investigation
Essential
- Adjusted calcium: <2.1 mmol/L
- PTH: LOW = hypoparathyroidism; HIGH = secondary HPT (vitamin D deficiency, CKD)
- Phosphate: high (hypoparathyroidism, CKD) vs low (vitamin D deficiency)
- Magnesium: check and replace if low
- 25-OH vitamin D: deficiency (<25 nmol/L), insufficiency (25-50 nmol/L)
- ALP: raised in vitamin D deficiency/osteomalacia (normal in hypoparathyroidism)
- U&Es: renal function (CKD)
- Albumin: for adjusted calcium calculation
Other
- ECG: prolonged QT
- X-ray: Looser zones (pseudofractures) in osteomalacia
- DEXA: if osteoporosis suspected
Management
Acute Severe Hypocalcaemia
- IV calcium gluconate 10%: 10mL (2.25 mmol) IV over 10 minutes → repeat if needed → continuous infusion (40mL in 500mL 0.9% NaCl over 24 hours)
- Cardiac monitoring: during IV calcium (risk of arrhythmia)
- IV magnesium: magnesium sulphate 8 mmol IV over 20 minutes if Mg²⁺ low
- Avoid IV calcium chloride peripherally (tissue necrosis if extravasation; use centrally if needed)
- Transition to oral calcium + vitamin D as soon as possible
Vitamin D Deficiency
- Loading: colecalciferol 50,000 IU weekly for 6 weeks (or equivalent); or fixed loading of 300,000 IU as split doses
- Maintenance: colecalciferol 800-2000 IU daily (NICE/SACN)
- Oral calcium supplementation if dietary intake inadequate
- Recheck 25-OH-D at 3 months
Hypoparathyroidism
- See separate topic: alfacalcidol/calcitriol + oral calcium
CKD
- Active vitamin D analogues (alfacalcidol/calcitriol)
- Phosphate binders
- Manage CKD-MBD as per NICE NG203
Referral Criteria
- Endocrinology: hypoparathyroidism, refractory hypocalcaemia
- Nephrology: CKD-related
- Gastroenterology: malabsorption
Prognosis
Vitamin D deficiency: excellent with supplementation; calcium normalises within weeks. Post-surgical hypoparathyroidism: transient resolves in days-weeks; permanent requires lifelong treatment. Chronic hypoparathyroidism: good quality of life achievable with monitoring. Severe acute hypocalcaemia: potentially fatal if untreated (laryngospasm, cardiac arrhythmia, seizures). Always responds to IV calcium.
Other Relevant Information
Approach to Hypocalcaemia
| PTH | Phosphate | Likely Diagnosis |
|---|---|---|
| LOW | HIGH | Hypoparathyroidism |
| HIGH | LOW | Vitamin D deficiency |
| HIGH | HIGH | CKD, pseudohypoparathyroidism |
IV Calcium Administration
| Preparation | Route | Notes |
|---|---|---|
| Calcium gluconate 10% | Peripheral IV | Safer; preferred |
| Calcium chloride 10% | Central line ONLY | 3× more elemental calcium; tissue necrosis if extravasation |