Acute Hypocalcaemia Protocol
What to give for a symptomatic low calcium now, and what to leave the patient on · v1.1- Enter the total calcium and albumin, the ionised calcium where you have it, the ECG findings, the neuromuscular symptoms and the magnesium.
- You get a stepwise replacement protocol with the agent, the route, the rate, magnesium co-correction where it is needed, and a monitoring plan.
- Check the magnesium first in a patient not responding to calcium.
- Repeat the sample from a fresh site if it came off a line running calcium. That blood will not tell you the patient's calcium.
- Children, and hypocalcaemia in the newborn.
- The cause of the low calcium. The differential on the Evidence tab is a prompt, not a pathway.
- Chronic hypoparathyroidism, which is a problem of months and years rather than of the next six hours.
- The acute pancreatitis, the sepsis or the massive transfusion that produced the number. It manages only the calcium that resulted from it.
1. Calcium & Albumin
2. Neuromuscular Status
3. Clinical Modifiers
Mechanisms, Doses and the Differential
1. The Albumin Correction: Why Total Calcium Lies
Approximately 40% of total serum calcium is bound to albumin, so in a hypoalbuminaemic patient the total reads falsely low while the physiologically active ionised calcium may be normal. Hypoalbuminaemia is common in Indian hospitals: malnutrition, nephrotic syndrome, cirrhosis, critical illness.
- Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)
- The formula is imprecise, and it is least reliable in exactly the patients who need it most.
- Measure ionised calcium directly wherever the machine is available: in ICU, on albumin infusions, and in any acid-base disturbance, where alkalosis lowers ionised calcium by increasing protein binding.
2. The Magnesium Gate: Why Calcium Will Not Rise Without Mg
Hypomagnesaemia causes hypocalcaemia twice over: it impairs PTH secretion from the parathyroid glands, and it causes skeletal resistance to PTH. The body cannot mount a PTH response, so the hypocalcaemia is refractory to calcium replacement until magnesium is corrected. It is the same magnesium gate that operates in hypokalaemia.
Rule: If hypocalcaemia is not responding to calcium replacement, check magnesium immediately. Correct Mg before giving more calcium.
3. IV Calcium: Gluconate Against Chloride
| Parameter | Calcium Gluconate 10% | Calcium Chloride 10% |
|---|---|---|
| Elemental Ca per 10 mL | 93 mg (2.3 mmol) | 272 mg (6.8 mmol) |
| Route | Peripheral or central IV | Central line ONLY |
| Extravasation risk | Low (mild irritation) | High: tissue necrosis and skin sloughing |
| Preferred setting | Ward, general use | Cardiac arrest, ICU with central access |
| Rate | 10 mL over 10 to 20 minutes | 10 mL over 10 to 20 minutes via central line |
| Equivalent volume | 10 mL is the reference dose | About 3 mL, not 10 mL |
The two are not interchangeable millilitre for millilitre. Read the row above before substituting one for the other. Ten millilitres of 10% calcium chloride carries about three times the elemental calcium of ten millilitres of 10% calcium gluconate, so a swap made by volume gives a threefold dose. The Society for Endocrinology sets the equivalence out in its 2019 addendum: 10 mL of 10% calcium gluconate is matched by 4.4 mL of 7.35% calcium chloride or 2.2 mL of 14.7% calcium chloride, which is about 3 mL of the 10% strength. Where the strength on the ampoule in your hand is none of these, calculate the volume, aiming at a loading bolus of 2.2 to 4.4 mmol of calcium followed by 1.1 to 2.2 mmol/hour.
Never push IV calcium rapidly. Rapid bolus can cause cardiac arrest (asystole). Always administer over 10 to 20 minutes with cardiac monitoring. Rapid rates are only permitted in cardiac arrest settings.
4. Post-Thyroidectomy Hypocalcaemia
The most common cause of acute symptomatic hypocalcaemia in Indian surgical wards, occurring in 20 to 30% of total thyroidectomies.
- Three mechanisms: inadvertent parathyroid removal, devascularisation of the parathyroid glands, and hungry bone syndrome, where the bones rapidly take up calcium once the PTH-driven resorptive stimulus is removed.
- Timing: typically 24 to 72 hours post-operatively. Most cases are transient, lasting weeks to months, but 1 to 2% become permanent.
- Prophylactic protocol: many centres now start empirical oral calcium (Calcium Carbonate 500 mg TDS or Shelcal-500) with Calcitriol 0.25 to 0.5 mcg BD immediately post-thyroidectomy in high-risk patients: total thyroidectomy, Graves disease, central neck dissection.
5. Chvostek and Trousseau Signs
| Sign | How it is elicited | What it is worth |
|---|---|---|
| Chvostek | Tapping the facial nerve anterior to the ear causes ipsilateral facial muscle twitching | Present in ~10% of normocalcaemic individuals. Low specificity |
| Trousseau | Inflating a BP cuff above systolic for 3 minutes causes carpopedal spasm: wrist flexion, MCP flexion, thumb adduction | More specific than Chvostek. Present in 94% of hypocalcaemic patients and only 1% of normocalcaemic individuals |
6. ECG Changes in Hypocalcaemia
| Finding | Mechanism | Clinical Significance |
|---|---|---|
| QTc prolongation (ST segment lengthening) | Delayed phase 2 (plateau) of action potential | Most common ECG change. QTc > 500 ms increases TdP risk. |
| T wave changes (peaked or inverted) | Altered repolarisation | Less specific. Compare with prior ECGs. |
| Bradycardia / heart block | Impaired conduction | Rare but reported in severe hypocalcaemia. |
| Torsades de Pointes (TdP) | Prolonged QT-triggered arrhythmia | Life-threatening. Treat with IV Mg + IV Ca + overdrive pacing. |
7. Differential Diagnosis of Hypocalcaemia
| Low PTH | High PTH | Other / Multifactorial |
|---|---|---|
| Post-surgical hypoparathyroidism | Vitamin D deficiency (most common globally) | Acute pancreatitis |
| Autoimmune hypoparathyroidism | CKD (impaired 1,25-D synthesis) | Sepsis / critical illness |
| Infiltrative (haemochromatosis, Wilson) | Pseudohypoparathyroidism (PTH resistance) | Massive blood transfusion (citrate) |
| Hypomagnesaemia (impairs PTH secretion) | Hyperphosphataemia (CKD, rhabdomyolysis, TLS) | Bisphosphonate / denosumab therapy |
| DiGeorge syndrome (congenital) | Hungry bone syndrome (post-parathyroidectomy) | Alkalosis (reduces ionised Ca) |
Abbreviations: ABG (Arterial Blood Gas) · BD (Twice Daily) · BP (Blood Pressure) · Ca (Calcium) · CKD (Chronic Kidney Disease) · D5W (5% Dextrose in Water) · ECG (Electrocardiogram) · eGFR (Estimated Glomerular Filtration Rate) · Fab (Fragment Antigen-Binding) · iCa (Ionised Calcium) · ICU (Intensive Care Unit) · IV (Intravenous) · MCP (Metacarpophalangeal) · Mg (Magnesium) · MgSO₄ (Magnesium Sulphate) · NS (Normal Saline) · PO₄ (Phosphate) · PPI (Proton Pump Inhibitor) · PTH (Parathyroid Hormone) · QTc (Corrected QT Interval) · RBC (Red Blood Cell) · TdP (Torsades de Pointes) · TDS (Three Times Daily) · TLS (Tumour Lysis Syndrome) · VT (Ventricular Tachycardia) · 25-OH (25-Hydroxy)
References
- Cooper MS, Gittoes NJL. Diagnosis and management of hypocalcaemia. BMJ. 2008;336(7656):1298-1302.
- Fong J, Khan A. Hypocalcemia: updates in diagnosis and management for primary care. Can Fam Physician. 2012;58(2):158-162.
- Brandi ML, Bilezikian JP, Shoback D, et al. Management of hypoparathyroidism: summary statement and guidelines. J Clin Endocrinol Metab. 2016;101(6):2273-2283.
- Kelly A, Levine MA. Hypocalcemia in the critically ill patient. J Intensive Care Med. 2013;28(3):166-177.
- Turner J, Gittoes N, Selby P; Society for Endocrinology Clinical Committee. Society for Endocrinology Endocrine Emergency Guidance: emergency management of acute hypocalcaemia in adult patients. Endocr Connect. 2016;5(5):G7-G8.
- Turner J, Gittoes N, Selby P. Addendum: dose equivalence of calcium gluconate and calcium chloride. Endocr Connect. 2019;8(6):X1.
- Khan AA, Bilezikian JP, Brandi ML, et al. Evaluation and management of hypoparathyroidism: summary statement and guidelines from the Second International Workshop. J Bone Miner Res. 2022;37(12):2568-2585.
- Bollerslev J, Rejnmark L, Marcocci C, et al. European Society of Endocrinology clinical guideline: treatment of chronic hypoparathyroidism in adults. Eur J Endocrinol. 2015;173(2):G1-G20.
- Ayuk J, Gittoes NJL. How should hypomagnesaemia be investigated and treated? Clin Endocrinol (Oxf). 2011;75(6):743-746.
- Radhakrishnan A, Chauhan I, Thakur JS, Azad R, Dhadwal M. Hypomagnesemia in post thyroidectomy patient: an underestimated entity. Indian J Otolaryngol Head Neck Surg. 2023;75(3):1986-1991.
- G R, Gupta A. Vitamin D deficiency in India: prevalence, causalities and interventions. Nutrients. 2014;6(2):729-775.
How to Cite This Tool
DOIhttps://doi.org/10.5281/zenodo.22401530
AMA Style:Umakanth S. Acute Hypocalcaemia Protocol. Version 1.1. MEDiscuss Clinical Decision Support System. Published 2026. Accessed . https://mediscuss.org/cdss/acute-hypocalcaemia. doi:10.5281/zenodo.22401530
Vancouver Style:Umakanth S. Acute Hypocalcaemia Protocol [Internet]. Version 1.1. MEDiscuss.org; 2026 [cited ]. Available from: https://mediscuss.org/cdss/acute-hypocalcaemia. doi:10.5281/zenodo.22401530
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Category Therapeutic & Management PathwaysProtocol
Specialties Internal Medicine, Endocrinology, Critical Care