Reasoning GP · Algorithm · 1-page summary
Hypocalcaemia in adults
For: adults with a low albumin-adjusted calcium (below the laboratory range), in hours or OOH. Not for: children (paediatric advice); hospital IV treatment (full algorithm, step 6); long-term hypoparathyroidism care (specialist plan, step 7).
Core rule: act on the albumin-adjusted calcium (ionised if unwell or discordant), never a raw total. Below 1.90 mmol/L, tetany, stridor, a seizure or marked QT prolongation is an emergency however well the patient seems. Check magnesium and PTH before replacing — calcium will not correct while magnesium is low.
0Stop — call 999 now — IV calcium gluconate is hospital-only
- Adjusted Ca²⁺ <1.90 mmol/L, even asymptomatic — oral calcium is too slow and unreliable → 999
- Tetany or carpopedal spasm, laryngospasm or stridor, hypocalcaemic seizure at any level → 999. Stridor with neck swelling after neck surgery may be a haematoma → 999 and urgent surgical/anaesthetic help.
- Marked QT prolongation, ventricular arrhythmia or syncope → 999 / same-day hospital
- While waiting: ECG — do not delay it for other results; no outpatient IV calcium. Other acute symptoms (perioral tingling, cramps) → Same-day hospital assessment with an ECG.
1Triage by adjusted calcium — mmol/L; symptoms override the number
| Adjusted Ca²⁺ | Action |
|---|---|
| <1.90, or symptoms | Severe — block 0. |
| 1.90–2.09 | Moderate → Same-day assessment, ECG and bloods. |
| 2.10–2.19, well | Mild → confirm on repeat; first-line bloods (block 3). |
| Low total, low albumin | Adjusted or ionised normal → not hypocalcaemia; no calcium. |
2Screen — one row is enough
- After thyroid or parathyroid surgery: new perioral tingling, paraesthesia, cramps or dysphonia → Same-day assessment and contact the operating team; tetany, stridor or seizure → 999
- Suspected acute pancreatitis → Same-day hospital admission whatever the calcium (<2.0 marks severe disease).
- Hypoparathyroidism, cannot keep calcium or calcitriol down (vomiting, diarrhoea) → Same-day: endocrine team or hospital.
- Cancer feature (bone pain, fracture, weight loss, raised ALP); ≥60 with persistent bone pain → offer FBC, calcium, ESR/PV, electrophoresis, free light chains → Suspected cancer pathway if myeloma (NG12).
3Assess — face to face; not by telephone
☐ Chvostek and Trousseau signs (more often positive when acute) ☐ ECG if symptomatic, acute or severe: prolonged QT/ST, bradycardia ☐ Repeat adjusted calcium with albumin (ionised if unwell or discordant), PTH, 25-OH vitamin D, phosphate, magnesium, U&E and eGFR ☐ If indicated: ALP, coeliac serology, cortisol
Not in primary care: IV calcium; calcitriol, alfacalcidol or PTH analogues unless under formal shared care.
4Classify by PTH — only once urgency is settled
- PTH low or inappropriately normal = hypoparathyroidism: post-surgical (commonest), autoimmune, magnesium depletion, infiltration, radiation → endocrinology.
- PTH high = secondary: vitamin D deficiency (commonest), CKD (phosphate high), malabsorption (coeliac, IBD, bariatric), pseudohypoparathyroidism.
- PTH suppressed: hungry bone, osteoblastic metastases, pancreatitis, tumour lysis, rhabdomyolysis.
- Low magnesium (alcohol, PPI, diuretic, diarrhoea) blocks PTH. Drugs: denosumab, bisphosphonates, cinacalcet.
- Uncertain or not responding to replacement → endocrinology; recheck magnesium first.
5Treat today — mild, asymptomatic, cause known
- Low magnesium: correct first (local formulary; hospital if severe, symptomatic or renal impairment); review the PPI.
- Vitamin D deficiency: local guidance (consider renal impairment, granulomatous disease, PHPT, stones); loading about 300,000 IU over 6–10 weeks, then maintenance. Calcium if intake poor.
- CKD: colecalciferol or ergocalciferol; alfacalcidol specialist-led (NG203).
- Before denosumab: calcium, renal function, vitamin D; correct first; calcium before each dose, plus within 2 weeks of the first dose if predisposed (CrCl <30). Doses: NICE/SPC, BNF, local formulary.
6Refer — by letter, after block 0–2
- Low PTH, pseudohypoparathyroidism, no response at 6 weeks → Urgent endocrinology.
- CKD with secondary hyperparathyroidism → renal. Malabsorption or positive coeliac serology → gastroenterology; keep eating gluten (NG20).
7Never reassure by — never leave <1.90 in an inbox overnight
- The patient looking well — below 1.90 is an emergency regardless.
- A low total calcium with a low albumin — adjust before prescribing.
- Calcium and vitamin D started with no magnesium or PTH checked.
- Perioral tingling within 72 hours of thyroidectomy — calcium until proven otherwise.
- Colecalciferol alone for low-PTH hypocalcaemia — needs specialist calcitriol.
- A normal-looking patient with symptoms but no ECG.
8Safety-net — say it, then document it
999 “Call 999 for spasm of the hands or feet that will not relax, a fit, difficult or noisy breathing, or palpitations with fainting or collapse.” Same-day “Contact us today for new tingling round the mouth or fingertips, or cramps — especially after neck surgery. With hypoparathyroidism, if you cannot keep your calcium or calcitriol down, contact the endocrine team or go to hospital.”
Remote or OOH: Chvostek, Trousseau and the QT cannot be assessed by phone — adjusted calcium below 2.10, or any symptom, needs face to face with an ECG.
✓Safe to manage in primary care only if — all five, documented
Adjusted 2.10–2.19 on a repeat; no block 0–2 row
Asymptomatic; ECG done if any symptom
Magnesium checked or corrected; renal function known
Cause identified — usually vitamin D, PTH high
Recheck at 2–4 weeks, named reviewer; safety-net
Summary of the full Reasoning GP hypocalcaemia algorithm, which holds the detail and evidence. Sources: Society for Endocrinology emergency guidance on acute hypocalcaemia (2016); NICE NG203, NG12 (updated April 2026), NG20; MHRA denosumab Drug Safety Update; KDIGO 2017 CKD–MBD; British Thyroid Association; SPS; product information. Clinical reference — follow local acute-transfer, renal and prescribing policies and check doses: NICE/SPC, BNF.