REASONING GP · Clinical algorithm · Quick reference

Hypocalcaemia in adults — triage and diagnostic approach

Correct for albumin, then decide urgency on symptoms and speed of fall. Vitamin D deficiency and post-surgical hypoparathyroidism are the common causes; check the magnesium, or replacement fails.

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AdultsLab resultAdjusted Ca²⁺ below 2.20v1.0 · Sep 2026

Core rule. Use the albumin-adjusted calcium — a low albumin is the commonest reason a total calcium looks low in a well patient. Below 1.90 mmol/L is an emergency at any level of wellness, and any tetany, seizure, laryngospasm, stridor or arrhythmia is an emergency whatever the number. Speed matters more than depth: an acute post-surgical fall causes symptoms at a level a dialysis patient tolerates. Two things get missed — a low magnesium, which blocks PTH release and makes replacement fail, and a prolonged QT, which is what kills.

On seeing the result: is this an emergency now? Arrange emergency admission — 999 or immediate discussion with the acute team

Adjusted Ca²⁺ below 1.90 mmol/L, however well the patient seems — IV calcium gluconate with cardiac monitoring is needed · any neuromuscular emergency at any level: carpopedal spasm or tetany, seizure, laryngospasm or stridor, bronchospasm, confusion · a prolonged QT, arrhythmia, bradycardia or hypotension · within days of thyroid, parathyroid or neck surgery with a falling calcium or new perioral tingling · after transfusion, or in acute pancreatitis, rhabdomyolysis or tumour lysis. Do an ECG. Hand over the adjusted calcium with albumin, magnesium, phosphate, U&E, the surgical history and drugs.

Adjust, grade, then send four tests Symptoms and tempo set urgency; PTH, magnesium, phosphate and vitamin D set the cause

Adjust first

Use the lab's albumin-adjusted calcium. A low albumin — nephrotic syndrome, liver disease, malnutrition, sepsis — makes the total read low while the ionised calcium is normal: that is not hypocalcaemia and needs no treatment. Confirm on a repeat unless symptoms demand action now.

Grade by adjusted value

Below 1.90: emergency admission at any level of wellness. 1.90–2.09: same-day — admission if symptomatic, post-surgical or with a long QT. 2.10–2.19: primary-care investigation. Symptoms and speed override the number: a post-operative patient at 2.00 falling fast beats a dialysis patient at 1.95 for years.

Send four tests together

PTH with a paired calcium · magnesium — the step most often omitted · phosphate · vitamin D (25-OH). Plus U&E and eGFR, albumin, ALP, and an ECG for the QT interval. Low PTH = hypoparathyroidism (post-surgical, autoimmune, magnesium-related). High PTH = a secondary response to vitamin D deficiency or CKD.

Symptoms to ask about

Perioral and fingertip tingling is the earliest and most useful — ask directly. Then cramps, carpopedal spasm, twitching, weakness; hoarseness or stridor; low mood, poor concentration, confusion; palpitations. Chronically: dry skin, brittle nails, cataracts, seizures.

Red-flag screen: trigger → concern → destination → what to do before handover One row is enough; do not add up reassuring features

Trigger / red flag	Leading concern · destination	Do now · do not delay
Adjusted Ca²⁺ below 1.90 mmol/L, however well the patient seems; or any level with tetany, carpopedal spasm, seizure, laryngospasm, stridor, bronchospasm or confusion.	Severe symptomatic hypocalcaemia · needs IV calcium gluconate with monitoring Emergency admission now	Oral calcium does not work fast enough here. Do an ECG and send it with the patient. Test and record Chvostek and Trousseau signs. Do not give IV calcium in the community unless trained and equipped with cardiac monitoring. Send the adjusted calcium with albumin, magnesium, phosphate and U&E.
Prolonged QT on ECG, arrhythmia, bradycardia, hypotension, new heart failure, or the patient takes digoxin or a QT-prolonging drug.	Ventricular arrhythmia · torsades de pointes Emergency admission now	The prolonged QT is what makes hypocalcaemia lethal, and it is invisible without an ECG — do one in every symptomatic patient. Review QT-prolonging drugs (macrolides, quinolones, antipsychotics, citalopram, ondansetron). Hypocalcaemia reduces the effect of digoxin, so the dose may become excessive once calcium is corrected — flag it.
Within days to weeks of thyroid, parathyroid or radical neck surgery, with a falling calcium, new perioral or fingertip tingling, or cramps — including after a recent discharge.	Post-surgical hypoparathyroidism · hungry bone syndrome Emergency admission if symptomatic or below 1.90 Same-day assessment and surgical team contact	The commonest cause of acute symptomatic hypocalcaemia, and the fall can be steep and early. Contact the operating team directly — they hold the calcium and alfacalcidol protocol. Do not start a supplement and review in a month. Perioral tingling after thyroidectomy is never "anxiety".
Acute precipitant: massive transfusion, acute pancreatitis, rhabdomyolysis, tumour lysis, severe sepsis, or a recent IV bisphosphonate or denosumab given without vitamin D repletion.	Acute chelation or sequestration · drug-induced severe hypocalcaemia Emergency admission now	Denosumab and IV bisphosphonates cause severe, sometimes life-threatening hypocalcaemia when vitamin D is deficient or eGFR is low — correct vitamin D and check calcium before giving them, and again after (MHRA). In tumour lysis and rhabdomyolysis the phosphate is high and calcium must not be replaced casually.
Adjusted Ca²⁺ 1.90–2.09 mmol/L in an alert patient without tetany or a long QT.	Moderate hypocalcaemia — assessment today Same-day assessment, ECG and bloods	Assess face to face: Chvostek and Trousseau signs, GCS, and an ECG for the QT. Send PTH with a paired calcium, magnesium, phosphate, vitamin D, U&E, albumin and ALP the same day. Start oral calcium if symptomatic, and repeat within 24–48 hours with a named person to check it.
Low magnesium, or a cause for it: proton pump inhibitor use, alcohol excess, diuretics, diarrhoea, malabsorption, refeeding, or a patient whose calcium fails to rise on adequate replacement.	Hypomagnesaemia blocking PTH secretion and action Same-day magnesium replacement and review of the cause	Hypocalcaemia will not correct while the magnesium is low, because magnesium is required for PTH release and end-organ response — this is the single commonest reason replacement appears to fail. Replace magnesium first or alongside. Long-term PPI use is a frequent and reversible cause; review the indication.
Malabsorption or nutritional cause: coeliac disease, IBD, bariatric or bowel surgery, chronic pancreatitis, alcohol excess, eating disorder, housebound or covered-skin vitamin D deficiency; or a high PTH with low vitamin D.	Severe vitamin D deficiency · osteomalacia · malabsorption Urgent investigation; admission if severe or symptomatic	Send coeliac serology, vitamin D, ALP, phosphate and PTH. A raised ALP with bone pain and proximal weakness suggests osteomalacia, which needs loading-dose vitamin D and follow-up, not a maintenance dose. Look for the malabsorption rather than treating the vitamin D level in isolation.
Hypocalcaemia with a cancer feature: unexplained bone pain, pathological fracture, weight loss, anaemia, unexplained renal impairment, a raised ALP, or hypocalcaemia during or after cancer treatment — particularly with a high phosphate or after denosumab.	Osteoblastic bone metastases · myeloma · tumour lysis Very urgent FBC, calcium, plasma viscosity/ESR and protein electrophoresis with Bence Jones protein — within 48 hours; urgent suspected-cancer referral if positive · NICE NG12	Hypocalcaemia is less often malignant than hypercalcaemia, but osteoblastic metastases (prostate, breast) and tumour lysis both consume calcium, and myeloma presents with bone pain, anaemia and renal impairment at any calcium level. NG12: in anyone 60 or over with a presentation consistent with possible myeloma, arrange a very urgent FBC, calcium, plasma viscosity or ESR and serum protein electrophoresis with urinary Bence Jones protein within 48 hours, and refer on the urgent suspected-cancer route if they suggest myeloma. Unexplained bone pain with a raised ALP also needs imaging.

Trigger / red flag

Leading concern · destination

Do now · do not delay

Adjusted Ca²⁺ below 1.90 mmol/L, however well the patient seems; or any level with tetany, carpopedal spasm, seizure, laryngospasm, stridor, bronchospasm or confusion.

Severe symptomatic hypocalcaemia · needs IV calcium gluconate with monitoring
Emergency admission now

Oral calcium does not work fast enough here. Do an ECG and send it with the patient. Test and record Chvostek and Trousseau signs. Do not give IV calcium in the community unless trained and equipped with cardiac monitoring. Send the adjusted calcium with albumin, magnesium, phosphate and U&E.

Prolonged QT on ECG, arrhythmia, bradycardia, hypotension, new heart failure, or the patient takes digoxin or a QT-prolonging drug.

Ventricular arrhythmia · torsades de pointes
Emergency admission now

The prolonged QT is what makes hypocalcaemia lethal, and it is invisible without an ECG — do one in every symptomatic patient. Review QT-prolonging drugs (macrolides, quinolones, antipsychotics, citalopram, ondansetron). Hypocalcaemia reduces the effect of digoxin, so the dose may become excessive once calcium is corrected — flag it.

Within days to weeks of thyroid, parathyroid or radical neck surgery, with a falling calcium, new perioral or fingertip tingling, or cramps — including after a recent discharge.

Post-surgical hypoparathyroidism · hungry bone syndrome
Emergency admission if symptomatic or below 1.90 Same-day assessment and surgical team contact

The commonest cause of acute symptomatic hypocalcaemia, and the fall can be steep and early. Contact the operating team directly — they hold the calcium and alfacalcidol protocol. Do not start a supplement and review in a month. Perioral tingling after thyroidectomy is never "anxiety".

Acute precipitant: massive transfusion, acute pancreatitis, rhabdomyolysis, tumour lysis, severe sepsis, or a recent IV bisphosphonate or denosumab given without vitamin D repletion.

Acute chelation or sequestration · drug-induced severe hypocalcaemia
Emergency admission now

Denosumab and IV bisphosphonates cause severe, sometimes life-threatening hypocalcaemia when vitamin D is deficient or eGFR is low — correct vitamin D and check calcium before giving them, and again after (MHRA). In tumour lysis and rhabdomyolysis the phosphate is high and calcium must not be replaced casually.

Adjusted Ca²⁺ 1.90–2.09 mmol/L in an alert patient without tetany or a long QT.

Moderate hypocalcaemia — assessment today
Same-day assessment, ECG and bloods

Assess face to face: Chvostek and Trousseau signs, GCS, and an ECG for the QT. Send PTH with a paired calcium, magnesium, phosphate, vitamin D, U&E, albumin and ALP the same day. Start oral calcium if symptomatic, and repeat within 24–48 hours with a named person to check it.

Low magnesium, or a cause for it: proton pump inhibitor use, alcohol excess, diuretics, diarrhoea, malabsorption, refeeding, or a patient whose calcium fails to rise on adequate replacement.

Hypomagnesaemia blocking PTH secretion and action
Same-day magnesium replacement and review of the cause

Hypocalcaemia will not correct while the magnesium is low, because magnesium is required for PTH release and end-organ response — this is the single commonest reason replacement appears to fail. Replace magnesium first or alongside. Long-term PPI use is a frequent and reversible cause; review the indication.

Malabsorption or nutritional cause: coeliac disease, IBD, bariatric or bowel surgery, chronic pancreatitis, alcohol excess, eating disorder, housebound or covered-skin vitamin D deficiency; or a high PTH with low vitamin D.

Severe vitamin D deficiency · osteomalacia · malabsorption
Urgent investigation; admission if severe or symptomatic

Send coeliac serology, vitamin D, ALP, phosphate and PTH. A raised ALP with bone pain and proximal weakness suggests osteomalacia, which needs loading-dose vitamin D and follow-up, not a maintenance dose. Look for the malabsorption rather than treating the vitamin D level in isolation.

Hypocalcaemia with a cancer feature: unexplained bone pain, pathological fracture, weight loss, anaemia, unexplained renal impairment, a raised ALP, or hypocalcaemia during or after cancer treatment — particularly with a high phosphate or after denosumab.

Osteoblastic bone metastases · myeloma · tumour lysis
Very urgent FBC, calcium, plasma viscosity/ESR and protein electrophoresis with Bence Jones protein — within 48 hours; urgent suspected-cancer referral if positive · NICE NG12

Hypocalcaemia is less often malignant than hypercalcaemia, but osteoblastic metastases (prostate, breast) and tumour lysis both consume calcium, and myeloma presents with bone pain, anaemia and renal impairment at any calcium level. NG12: in anyone 60 or over with a presentation consistent with possible myeloma, arrange a very urgent FBC, calcium, plasma viscosity or ESR and serum protein electrophoresis with urinary Bence Jones protein within 48 hours, and refer on the urgent suspected-cancer route if they suggest myeloma. Unexplained bone pain with a raised ALP also needs imaging.

Safety rule. Never act on the total calcium — use the albumin-adjusted value; a low albumin with a normal ionised calcium is not hypocalcaemia. Wellness is not reassurance below 1.90. Do an ECG in every symptomatic patient — the QT is what kills. Check and replace magnesium, or the calcium will not rise. Correct vitamin D before denosumab or an IV bisphosphonate.

Colour is semantic: red = emergency now · amber = same-day assessment · blue = define/assess · green = primary-care management · purple = uncertain / specialist route (including 2WW). Continued on page 2: investigation, classification, cause classifier, routine referral, primary-care management, endpoint.

REASONING GP · Hypocalcaemia in adults — triage and diagnostic approach

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Assessment and investigation Neuromuscular signs and the QT cannot be assessed remotely

Assess

GCS; Chvostek sign (facial twitch on tapping the facial nerve) and Trousseau sign (carpal spasm with a cuff above systolic for 3 min — more specific); voice, stridor, neck scar.

ECG — in every symptomatic patient

Look for a prolonged QT, which carries the arrhythmia risk; also bradycardia and heart block. Review QT-prolonging drugs alongside — the ECG is not optional here.

The bloods

Adjusted calcium with albumin · PTH paired with calcium · magnesium · phosphate · vitamin D · U&E · ALP · FBC · coeliac serology if malabsorption is possible · and in the 60-and-overs, electrophoresis with Bence Jones protein (NG12).

Reading them together

Low PTH: hypoparathyroidism — post-surgical, autoimmune or magnesium-driven. High PTH, low vitamin D: deficiency or malabsorption. High PTH, high phosphate, low eGFR: CKD; with normal renal function, pseudohypoparathyroidism.

Classify: three exits, not two A low total calcium with a low albumin is not a diagnosis — it is an artefact

Emergency or same-day

Below 1.90, any tetany, seizure, laryngospasm or long QT, post-surgical, an acute precipitant, or 1.90–2.09 today. Output: destination, adjusted calcium, magnesium, phosphate, ECG, surgical history.

Mild, cause known, managed

Adjusted Ca²⁺ 2.10–2.19, asymptomatic, normal QT and magnesium, clear cause — usually vitamin D deficiency with a high PTH. Output: cause, replacement, recheck date, thresholds.

Unclassified or unexplained

Low PTH with no surgical history, calcium not rising on replacement, a high phosphate with normal renal function, or unexplained bone pain. Output: state the uncertainty, take the §6 route or NG12 panel.

Cause classifier: the PTH splits it, then the magnesium and phosphate Only once the urgency is settled

Vitamin D deficiency and malabsorption
PTH high, vitamin D low

The commonest cause in the community: limited sun exposure, covered or darker skin, housebound or care-home residence, obesity, pregnancy, malabsorption (coeliac, IBD, bariatric surgery, pancreatitis), anticonvulsants. Phosphate low or normal; a raised ALP with bone pain and proximal weakness means osteomalacia.

Hypoparathyroidism
PTH low or inappropriately normal

Post-surgical (thyroid, parathyroid, neck) is much the commonest, transient or permanent — check the operation date. Also autoimmune, infiltration, radiation, and magnesium-related, which is reversible. A low PTH with a high phosphate is the classic pattern; needs endocrine input.

Hypomagnesaemia

Blocks PTH secretion and its end-organ effect, so calcium will not correct until magnesium does — the commonest reason replacement fails. Causes: proton pump inhibitors (long-term and forgotten), alcohol, diuretics, diarrhoea, malabsorption, refeeding. Replace magnesium first or alongside.

CKD, drugs and acute precipitants

CKD — PTH high, phosphate high: reduced 1-alpha-hydroxylation with phosphate retention, managed with alfacalcidol or calcitriol, not plain colecalciferol alone which cannot be activated, alongside phosphate control under renal guidance (NG203). Drugs: denosumab and IV bisphosphonates — severe hypocalcaemia if vitamin D is deficient or eGFR low, so correct and check before giving (MHRA) · PPIs via magnesium · loop diuretics, foscarnet, phenytoin. Acute: massive transfusion (citrate), pancreatitis, rhabdomyolysis, tumour lysis, sepsis, hyperventilation.

Artefact, and what not to conclude

Artefact: a low albumin with a normal ionised calcium — no treatment · a contaminated or EDTA sample · respiratory alkalosis. Do not conclude: "vitamin D deficiency" without a PTH and magnesium · "post-surgical, settled" without a recheck · "anxiety" for tingling after neck surgery.

Refer routinely from this consultation Not same-day — the cases that leave by letter; §7 is what primary care does today

Confirmed hypoparathyroidism — a low or inappropriately normal PTH — → endocrinology; not a primary-care diagnosis to manage alone, needing activated vitamin D (alfacalcidol or calcitriol), calcium titration and monitoring for hypercalciuria and renal calcification · post-surgical hypocalcaemia persisting beyond a few weeks → the operating team and endocrinology jointly · suspected pseudohypoparathyroidism → endocrinology · hypocalcaemia in CKD → renal, for activated vitamin D and phosphate management (NG203) · positive coeliac serology → gastroenterology, without starting a gluten-free diet first (NG20) · confirmed osteomalacia → metabolic bone clinic · recurrent hypocalcaemia on denosumab → discuss with the prescriber before the next dose.

The only decisions that belong in this consultation What primary care manages today — mild, asymptomatic hypocalcaemia from vitamin D deficiency

Confirm on the adjusted value, then send four tests and an ECG

Repeat the calcium with albumin, and send PTH with a paired calcium, magnesium, phosphate and vitamin D together — not sequentially over months. Add U&E, ALP, FBC, coeliac serology where indicated, and an ECG if there is any symptom. A low total with a low albumin and no symptoms needs no treatment.

Replace magnesium first, then the vitamin D

Magnesium first: if it is low, correct it before expecting any calcium response — oral for mild deficiency, IV via the acute route if severe — and review the cause, stopping or reducing the proton pump inhibitor where the indication no longer holds. Then the vitamin D: a loading regimen of colecalciferol (about 300,000 units total over 6–10 weeks in divided doses) then maintenance, per local formulary — a maintenance dose alone corrects deficiency too slowly. Add oral calcium if dietary intake is poor or symptoms are present. Recheck at 4–8 weeks and look for the malabsorption behind it. Before denosumab or an IV bisphosphonate, every time: check calcium and correct vitamin D before each dose and check calcium after, particularly where eGFR is reduced (MHRA) — never give the next dose with an uncorrected calcium.

Recheck and the escalation rule — write it down

Repeat adjusted calcium, magnesium and U&E at 1–2 weeks after starting replacement, then 4–8 weeks, then widening intervals. Write the triggers down: below 1.90, or any tetany, spasm, seizure, stridor or long QT → emergency admission; 1.90–2.09, or new symptoms → same-day assessment.

What not to do

Do not act on a total calcium with a low albumin, start calcium without checking magnesium and PTH, give plain colecalciferol alone in CKD (it cannot be activated), manage confirmed hypoparathyroidism in primary care, attribute post-thyroidectomy tingling to anxiety, or skip the ECG.

Endpoint and documentation Finish with one of four conclusions

1 · Emergency

Admission arranged; adjusted calcium with albumin, magnesium, phosphate, signs, ECG and QT, surgical history, drugs.

2 · Same-day

Assessment today; Chvostek and Trousseau recorded; ECG done; PTH, magnesium, phosphate, vitamin D sent; oral calcium if symptomatic; repeat in 24–48 h.

3 · Mild, cause known, managed

Adjusted level, PTH, magnesium and vitamin D recorded; loading regimen started; PPI addressed; recheck date and thresholds written down.

4 · Unclassified or unexplained

Uncertainty stated; §6 referral or NG12 48-hour panel sent, with date; interim replacement; review owner.

Why primary-care management is safe today, in one line: the value is the albumin-adjusted one, confirmed on a repeat · 2.10–2.19 mmol/L · asymptomatic — no tingling, cramps, spasm or hoarseness · Chvostek and Trousseau negative · ECG normal with a normal QT where a symptom was reported · magnesium normal or corrected · PTH high with low vitamin D, so hypoparathyroidism is not in play · no recent neck surgery, no denosumab due · cause identified, replacement started · recheck at 1–2 weeks with a named reviewer and written thresholds. Safety-net: contact us or 111 the same day for tingling round the mouth or fingers, cramps or spasms in hands or feet, a hoarse voice, palpitations or confusion; call 999 for a fit, a spasm you cannot relax, or difficulty breathing.

Remote and result-handling limitation. Chvostek and Trousseau signs and the QT cannot be assessed on the telephone, so an adjusted calcium below 2.10, or any symptom, needs a face-to-face assessment with an ECG — and a calcium below 1.90 must never sit in an inbox overnight.

Clinical decision support only; follow local acute-transfer, renal and prescribing policies and check doses against the current BNF. Source hierarchy: NICE guidelines and CKS first, then BNF/MHRA for doses and safety, then national specialty guidance. Sources: NICE NG203 Chronic kidney disease · NG146 Osteoporosis · NG12 Suspected cancer (May 2025) · NG20 Coeliac disease · NICE CKS Hypocalcaemia, Vitamin D deficiency in adults · MHRA Drug Safety Update: denosumab — severe hypocalcaemia risk · Society for Endocrinology emergency guidance on acute hypocalcaemia · UK Kidney Association · BNF · SACN vitamin D guidance. Review after any guidance or medicines-safety update, otherwise every 6 months. © Reasoning GP · gpreasoning.uk