⚠️ Always check magnesium in hypocalcaemia. Hypomagnesaemia can both reduce PTH secretion and cause end-organ resistance to PTH, making hypocalcaemia refractory until Mg²⁺ is corrected.

🚨 Acute / Severe Hypocalcaemia: Initial Management Always ask: Is the patient symptomatic? Are they on digoxin? Is magnesium low?
🩺 ABCDE assessment and place in an appropriate monitored setting. 📈 ECG monitoring if severe, symptomatic, arrhythmia risk, or IV calcium is being given. 🧪 Send/confirm: adjusted calcium, ionised calcium if critically unwell, Mg²⁺, phosphate, PTH, U&E, vitamin D. 💉 If adjusted Ca <1.9 mmol/L or symptomatic at any subnormal level: Give 10–20 mL of 10% calcium gluconate IV diluted in 50–100 mL compatible fluid and infuse over about 10 minutes with ECG monitoring. 🔁 If symptoms persist or recur, the bolus may be repeated and followed by continuous infusion. 💧 Typical infusion: 100 mL of 10% calcium gluconate in 1 L 0.9% saline or 5% dextrose, rate titrated to response (commonly around 50–100 mL/hour depending on local protocol). 🧂 Correct hypomagnesaemia promptly if present, otherwise calcium may not normalise. 💊 Treat the cause: e.g. vitamin D deficiency, hypoparathyroidism, CKD, pancreatitis, sepsis, drug-related causes. 🌞 Step-down therapy: oral calcium once stable; add alfacalcidol/calcitriol when hypoparathyroidism or impaired vitamin D activation is likely. ⚠️ Digoxin caution: IV calcium may increase arrhythmia risk in digoxin toxicity; senior/cardiology input is sensible unless treatment is immediately life-saving. 🚑 Urgent senior/ICU input if there is stridor, laryngospasm, seizures, marked tetany, haemodynamic instability, or serious arrhythmia. 💥 Extravasation risk: calcium is irritant to tissues - use a good large-bore cannula/large vein and check the line carefully.

🚨 Acute / Severe Hypocalcaemia: Initial Management
Always ask: Is the patient symptomatic? Are they on digoxin? Is magnesium low?

🩺 ABCDE assessment and place in an appropriate monitored setting.
📈 ECG monitoring if severe, symptomatic, arrhythmia risk, or IV calcium is being given.
🧪 Send/confirm: adjusted calcium, ionised calcium if critically unwell, Mg²⁺, phosphate, PTH, U&E, vitamin D.
💉 If adjusted Ca <1.9 mmol/L or symptomatic at any subnormal level:
Give 10–20 mL of 10% calcium gluconate IV diluted in 50–100 mL compatible fluid and infuse over about 10 minutes with ECG monitoring.
🔁 If symptoms persist or recur, the bolus may be repeated and followed by continuous infusion.
💧 Typical infusion: 100 mL of 10% calcium gluconate in 1 L 0.9% saline or 5% dextrose, rate titrated to response (commonly around 50–100 mL/hour depending on local protocol).
🧂 Correct hypomagnesaemia promptly if present, otherwise calcium may not normalise.
💊 Treat the cause: e.g. vitamin D deficiency, hypoparathyroidism, CKD, pancreatitis, sepsis, drug-related causes.
🌞 Step-down therapy: oral calcium once stable; add alfacalcidol/calcitriol when hypoparathyroidism or impaired vitamin D activation is likely.
⚠️ Digoxin caution: IV calcium may increase arrhythmia risk in digoxin toxicity; senior/cardiology input is sensible unless treatment is immediately life-saving.
🚑 Urgent senior/ICU input if there is stridor, laryngospasm, seizures, marked tetany, haemodynamic instability, or serious arrhythmia.
💥 Extravasation risk: calcium is irritant to tissues - use a good large-bore cannula/large vein and check the line carefully.

🔢 Corrected / Adjusted Calcium Ranges

Category	Adjusted Ca (mmol/L)
✅ Normal	About 2.20–2.60
⬇️ Mild hypocalcaemia	1.90–2.19 and asymptomatic
🚨 Severe hypocalcaemia	<1.90 or symptomatic at any level below normal

📌 Use adjusted calcium for routine interpretation, but consider ionised calcium in critical illness, major acid–base disturbance, or when albumin makes total calcium misleading.

🧬 Aetiology & Pathophysiology

⚡ Low extracellular Ca²⁺ lowers the threshold for membrane depolarisation, causing neuromuscular hyperexcitability → paraesthesia, tetany, carpopedal spasm, laryngospasm, and seizures.
❤️ Cardiac repolarisation is prolonged, producing a long QT interval and increasing arrhythmia risk.
🧂 Mg²⁺ deficiency is important because it can cause both impaired PTH release and PTH resistance.

📊 Common Causes of Hypocalcaemia

Cause	Typical Clues	Biochemistry Pattern	Management Principles
Hypoparathyroidism (post-thyroid/parathyroid surgery, autoimmune, infiltrative)	Perioral tingling, tetany, post-op neck surgery	Low Ca, low or inappropriately normal PTH, often high phosphate	Calcium ± alfacalcidol/calcitriol; treat acute episodes with IV calcium if severe
Vitamin D deficiency	Bone pain, proximal myopathy, osteomalacia/rickets risk	Low/low-normal Ca, low vitamin D, raised PTH, often low phosphate	Vitamin D replacement ± calcium
CKD / reduced 1α-hydroxylation	Renal disease, CKD-MBD features	Low Ca, high phosphate, raised PTH, reduced active vitamin D	Manage CKD-MBD, phosphate control, active vitamin D analogues, calcium as needed
Hypomagnesaemia	Alcohol excess, diarrhoea, PPIs, diuretics, aminoglycosides	Low Mg, low Ca, PTH low or inappropriately normal	Replace Mg first / alongside Ca
Acute pancreatitis	Severe epigastric pain, vomiting	Low Ca, raised amylase/lipase	Supportive pancreatitis care; calcium if severe/symptomatic
Pseudohypoparathyroidism	Possible Albright hereditary osteodystrophy phenotype	Low Ca, high PTH, high phosphate	Calcium + active vitamin D; endocrine follow-up
Drugs (bisphosphonates, denosumab, cisplatin, foscarnet, anticonvulsants, cinacalcet)	Temporal relationship to treatment	Variable, depending on mechanism	Stop/review culprit drug, replace calcium ± Mg/vitamin D
Sepsis / critical illness	Shock, organ dysfunction	Low Ca in context of severe illness	Treat underlying illness; reserve IV calcium for severe/symptomatic cases
Hungry bone syndrome	After parathyroid surgery, high bone turnover states	Marked/prolonged low Ca ± low Mg ± low phosphate	Aggressive calcium replacement + active vitamin D
Massive transfusion / citrate load	Major haemorrhage / blood product exposure	Low ionised calcium	Correct as part of major haemorrhage management

⚡ Clinical Features

Acute: Perioral/fingertip paraesthesia, muscle cramps, carpopedal spasm, tetany, positive Trousseau’s/Chvostek’s sign, laryngospasm/stridor, seizures, prolonged QT.
Chronic: Cataracts, dry skin, brittle nails, poor dentition, basal ganglia calcification, neuropsychiatric symptoms.

🧪 Investigations

First-line bloods: adjusted calcium, albumin, Mg²⁺, phosphate, U&E/creatinine, PTH, 25-OH vitamin D.
Consider ionised calcium if critically ill or the total/adjusted calcium may be unreliable.
ECG: prolonged QT ± arrhythmia.
Think about cause: recent thyroid/parathyroid surgery, CKD, pancreatitis, malabsorption, alcohol excess, blood transfusion, denosumab/bisphosphonate use, PPIs.

📈 Interpretation Patterns

Low Ca + low / inappropriately normal PTH → hypoparathyroidism or severe hypomagnesaemia.
Low Ca + high PTH → vitamin D deficiency, CKD, pseudohypoparathyroidism, pancreatitis, sepsis, or other secondary causes.
Low Ca + low Mg → correct Mg early, as calcium may remain refractory otherwise.
Low Ca + high phosphate → think hypoparathyroidism, CKD, or pseudohypoparathyroidism.

💊 Practical Management Summary

Mild, asymptomatic hypocalcaemia (1.9–2.19 mmol/L): oral calcium, investigate cause, recheck calcium after correction begins.
Severe or symptomatic hypocalcaemia: IV calcium gluconate with monitoring, then infusion if needed.
Correct magnesium and address the underlying pathology.
Use active vitamin D when hypoparathyroidism or impaired renal activation is likely.
Avoid rapid IV administration because it can cause flushing, nausea, hypotension, and arrhythmias.

📚 References

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Hypocalcaemia ✅