Hypocalcaemia Severity Interpreter

Q: What calcium level counts as severe hypocalcaemia?

On UK guidance, an albumin-corrected calcium below 1.90 mmol/L (7.6 mg/dL) — and, just as importantly, symptomatic hypocalcaemia at any level below the reference range. The Society for Endocrinology's emergency guidance defines severe as "Serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range", and NHS Greater Glasgow and Clyde and York and Scarborough both use the same cut with mild as 1.90 to 2.19 mmol/L and asymptomatic. US sources put the threshold lower, at under 7 mg/dL (1.75 mmol/L), so a calcium of 1.80 mmol/L is severe on one scale and not on the other. This page uses the UK cut because it is more cautious and because it captures symptomatic patients whose number looks mild.

Q: Why does my calcium not come up despite replacement?

The commonest reversible answer is magnesium. Hypomagnesaemia causes a functional hypoparathyroidism — resistance to PTH at the tissues and, when severe, impaired PTH secretion — and the standard statement is that "correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal". Even after replacement starts, "hypocalcemia may not be corrected for 3-7 days", because magnesium is predominantly an intracellular cation and cellular uptake is slow, so a serum magnesium that has normalised does not mean the deficit is filled. Look for the cause too: proton pump inhibitors, loop and thiazide diuretics, aminoglycosides, alcohol excess, malabsorption and chronic diarrhoea. Vitamin D deficiency and untreated hypoparathyroidism are the other reasons replacement underperforms.

Q: How reliable are Chvostek's and Trousseau's signs?

They are not equivalent. Trousseau's sign — carpopedal spasm after inflating a cuff 20 mmHg above systolic for two to three minutes — has a reported sensitivity of 94% and specificity of 99%, with a positive sign in only 1% to 4% of healthy people, and is worth eliciting. Chvostek's sign is much weaker: a positive sign can be elicited in 25% of healthy individuals, 29% of hypocalcaemic patients do not produce one, and a population-based study found a positive sign became more likely as calcium rose, by about 4% per mg/dL. Its own reference chapter concludes that the association with hypocalcaemia has been accepted "despite very little literature supporting this claim". Diagnose on the corrected calcium and get a 12-lead ECG for QT prolongation.

Q: What ECG change does hypocalcaemia cause?

QT prolongation, produced by lengthening of the ST segment rather than by a change in the T wave itself. It is "fairly common in hypocalcemic patients" and matters because a prolonged QTc may predispose to torsades de pointes. A 12-lead ECG belongs in the initial assessment of any significant hypocalcaemia, and ECG monitoring is part of the published treatment: intravenous calcium gluconate is given "over 10 min with ECG monitoring" and repeated until the patient is asymptomatic.

Q: Should calcium be corrected for albumin before grading a hypocalcaemia?

Yes, and the reason is the opposite of the one that applies in hypercalcaemia. About 40% of total calcium is albumin-bound and inactive, so a low albumin lowers the measured total calcium without lowering the ionised fraction — it creates a hypocalcaemia that is not physiologically real. In a hospital population, low albumin is the commonest reason for a total calcium below the reference interval, so grading an uncorrected value overstates the severity and can lead to treating an artefact. Use the corrected calcium calculator, and measure an ionised calcium where the answer will change management, because the correction formula is unreliable in critical illness, chronic kidney disease and after major surgery.

Q: What is the first test in a hypocalcaemia workup?

PTH and magnesium, on the same request, before treatment starts. The PTH is the classical branch point: low or inappropriately within the reference range means the parathyroid gland is the problem, with post-surgical hypoparathyroidism much the commonest; raised means the gland is responding correctly and the problem is downstream, with vitamin D deficiency at the top of that list. The magnesium comes with it because hypomagnesaemia mimics hypoparathyroidism exactly — it causes a functional, fully reversible PTH deficiency and resistance — so a low PTH cannot be interpreted until the magnesium is known. Send phosphate, renal function and a 25-hydroxyvitamin D alongside them.

Q: Can someone have symptoms of hypocalcaemia with a normal calcium?

Yes, and the classical example is acute hyperventilation. Respiratory alkalosis raises the pH, which drives calcium onto albumin and lowers the ionised fraction while the total calcium stays completely normal — producing perioral and peripheral paraesthesiae and carpopedal spasm in someone whose calcium result is unremarkable. It needs no calcium replacement. The converse also happens: acidosis displaces calcium from albumin and raises the ionised fraction, which can mask a real hypocalcaemia on an ionised measurement taken during acidaemia.

Grade a hypocalcaemia on albumin-corrected calcium in mmol/L and mg/dL, with both published severity sets attributed, the clinical state outranking the number, and the two results that change management built in — the PTH branch and the magnesium.

Last updated 18 Sep 2026

Corrected calcium, clinical state, PTH and magnesium

Corrected calcium + state + PTH + Mg

Unit of the calcium resultCalcium’s atomic weight is 40.078, so 1 mmol/L is 4.0078 mg/dL. The round numbers in the two conventions are therefore not equivalent: 1.90 mmol/L is 7.61 mg/dL, and the US severe threshold of 7 mg/dL is 1.747 mmol/L. Watch for mEq/L on older reports as well — calcium is divalent, so mEq/L is twice mmol/L and entering it as mmol/L doubles the result.

Albumin-corrected total calciumThe ALBUMIN-CORRECTED (adjusted) calcium, not the raw total. About 40% of total calcium is albumin-bound and inactive, so the correction has to happen before the classification. The corrected calcium calculator does it and sets out where the formula fails. Note that hypoalbuminaemia lowers the total calcium without lowering the ionised fraction, so an uncorrected value in a sick patient overstates the hypocalcaemia — the opposite of the error it causes in hypercalcaemia.

Ionised calciumOnly the ionised fraction is metabolically active, and a measured ionised calcium is the benchmark: the albumin correction “is not a completely precise method, and serum ionized calcium measurements can confirm whether true hypocalcemia is present”. Answering ‘measured and normal’ overrides every band below. The sample is unforgiving — delay or air exposure loses carbon dioxide, the pH rises, calcium binds to albumin and the measured value falls spuriously, so the handling error runs towards a falsely low result.

Clinical stateThis selector sits above the numeric bands deliberately, and the published definition of severe hypocalcaemia puts it there: “<1.9 mmol/L and/or symptomatic at any level below reference range”. Symptoms track the RATE of fall as much as the level — presentation “depends on the rate of onset and chronicity of hypocalcemia”, and the threshold at which symptoms appear “varies depending on how quickly levels fall”. The single most useful extra piece of information is a previous calcium.

PTH resultThe first branch of the workup. A normal gland raises PTH in response to a low calcium, so a PTH merely within the reference interval alongside hypocalcaemia is inappropriately normal and counts as low. Low or inappropriately normal points to hypoparathyroidism — post-surgical above all — and raised points downstream to vitamin D deficiency, malabsorption, chronic kidney disease or pseudohypoparathyroidism. Many laboratories need a separate EDTA sample; send it before treatment starts.

MagnesiumThis sits ABOVE the PTH branch in the logic, and that is a clinical claim rather than a layout choice. Hypomagnesaemia causes a functional hypoparathyroidism — resistance to PTH, and impaired PTH secretion when severe — so while the magnesium is low the PTH result cannot be interpreted and the calcium will not correct. “Correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal.”

Severe hypocalcaemia — below 1.90 mmol/L (7.6 mg/dL)Example

Albumin-corrected calcium 1.78 mmol/L two days after total thyroidectomy. Perioral paraesthesiae and cramps. PTH low. Magnesium not yet sent. Ionised calcium not measured

Correct it, then grade it, then branch

1. Adjust the total calcium for albumin — before anything else.
2. Grade it: severe is below 1.90 mmol/L (7.6 mg/dL) and/or symptomatic at any level below the reference range; mild is 1.90 to 2.19 mmol/L and asymptomatic.
3. Check the magnesium, because a low one makes the calcium uncorrectable and the PTH uninterpretable.
4. Then branch on the PTH: low or inappropriately normal → the gland; raised → downstream.

mmol/L to mg/dL: multiply by 4.0078, from calcium’s atomic weight of 40.078. So 1.90 mmol/L = 7.61 mg/dL, and the US severe threshold of 7 mg/dL = 1.747 mmol/L — the two published severe cuts are 0.15 mmol/L apart
Symptomatic at any level: the Society for Endocrinology’s definition of severe hypocalcaemia is “Serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range”. The second clause is not a footnote — it is why a symptomatic patient at 2.05 mmol/L is treated as severe
The rate of fall: symptoms depend on “the rate of onset and chronicity of hypocalcemia” and the threshold at which they appear “varies depending on how quickly levels fall”. A previous calcium is worth more than any single value
The magnesium trap: “correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal”, and even then “hypocalcemia may not be corrected for 3-7 days”, because magnesium is predominantly intracellular and cellular uptake is slow

Worked example

Albumin-corrected calcium 1.78 mmol/L two days after total thyroidectomy. Perioral paraesthesiae and cramps. PTH low. Magnesium not yet sent. Ionised calcium not measured
The calcium has already been adjusted for albumin, which is the step that has to come first
1.78 mmol/L is below 1.90, so it is severe on the UK band set — and it would be severe anyway on the second clause of the same definition, because the patient is symptomatic
1.78 mmol/L is 7.13 mg/dL. On the US threshold of under 7 mg/dL this would be just outside the severe band, which is the disagreement this page shows rather than hides
Treat now: 10–20 mL of 10% calcium gluconate in 50–100 mL of 5% dextrose intravenously over 10 minutes with ECG monitoring, repeated until asymptomatic, then a titrated infusion. Get a 12-lead ECG for QT prolongation
The PTH is low two days after thyroid surgery → post-surgical hypoparathyroidism, much the commonest cause of a low PTH
The magnesium has not been sent. Until it is, that low PTH cannot be taken at face value: hypomagnesaemia causes a functional hypoparathyroidism indistinguishable from the real thing on a PTH result, and the calcium will not correct until the magnesium does
Do not reach for Chvostek's sign to settle any of this. It is positive in 25% of healthy people and negative in 29% of hypocalcaemic ones

The two published severity sets, and where they disagree

The bands on this page are the UK set, because it is the more cautious of the two and because its second clause — symptomatic at any level below the reference range — captures the patients a purely numeric scale misses. The disagreement is real and worth knowing: a calcium of 1.80 mmol/L is severe in the UK and not severe on the US cut, and neither body has made an error. Your laboratory’s own lower reference limit governs where hypocalcaemia begins at all, and it is not always 2.20 mmol/L.
Severity	UK — Society for Endocrinology and NHS guidance	US — StatPearls	Agree?
Mild	1.90–2.19 mmol/L (7.6–8.8 mg/dL) and asymptomatic	No mild band defined; normal total calcium given as 8.5–10.5 mg/dL (2.12–2.62 mmol/L)	Not comparable — the UK set defines a band, the US source defines only a normal range and a severe cut
Severe	Below 1.90 mmol/L (7.6 mg/dL) and/or symptomatic at any level below the reference range	Below 7 mg/dL (1.75 mmol/L)	No — 1.75 to 1.90 mmol/L is severe to one and not to the other
Symptoms at any level	Counts as severe, explicitly	Not stated as a criterion	No
Lower limit of normal	2.20 mmol/L (8.8 mg/dL) implied by the mild band	8.5 mg/dL (2.12 mmol/L)	No — 0.08 mmol/L apart

The two signs, and what they are actually worth

Chvostek’s sign is one of the most durable pieces of clinical folklore in medicine, and its own StatPearls chapter concludes that the association with hypocalcaemia “has long been accepted in the medical community, despite very little literature supporting this claim”. A quarter of well people have it, nearly a third of hypocalcaemic people do not, and the population association runs in the wrong direction. Trousseau’s sign is worth eliciting. The emergency, however, is diagnosed on the calcium and on the ECG.
Sign	How it is elicited	Performance
Trousseau’s	Inflate a blood pressure cuff 20 mmHg above systolic for 2–3 minutes; carpopedal spasm — flexion of the wrist and metacarpophalangeal joints, extension of the interphalangeal joints, adduction of the thumb	Reported sensitivity 94% and specificity 99%; positive in “up to 1% to 4% of healthy individuals”. The more useful of the two
Chvostek’s	Tap over the facial nerve just anterior to the external auditory meatus; ipsilateral facial muscle contraction	Positive in 25% of healthy individuals; 29% of hypocalcaemic patients are negative; a population study found a positive sign became more likely as calcium rose, by 4% per mg/dL. Endotext gives a lower false-positive figure of 10%
ECG	12-lead	QT prolongation from lengthening of the ST segment is “fairly common in hypocalcemic patients” and may predispose to torsades de pointes. This is the test that tells you the hypocalcaemia is dangerous

The first branch: PTH-deficient or PTH-driven

Magnesium appears in the first row for a reason that is easy to miss: hypomagnesaemia produces a functional hypoparathyroidism through PTH resistance and, when severe, impaired secretion, so it is indistinguishable from true hypoparathyroidism on a PTH result alone. It is also the one cause in that row that is fully reversible, which is why a magnesium belongs on the same request form as the PTH. The PTH converter explains why a PTH cannot be compared between laboratories.
PTH	What it means	Causes to work through	Next tests
Low, or inappropriately within the reference range	The gland is the problem. A normal gland RAISES PTH when calcium falls, so a normal PTH here is abnormal	Post-surgical hypoparathyroidism (much the commonest); autoimmune; infiltrative or radiation damage; DiGeorge and activating calcium-sensing receptor mutations; hypomagnesaemia, which mimics all of them	Magnesium first, then phosphate (typically high), renal function, and an operative history
Raised	The gland is responding correctly and the problem is downstream	Vitamin D deficiency (commonest); malabsorption; chronic kidney disease; pseudohypoparathyroidism; acute pancreatitis; tumour lysis; rhabdomyolysis; citrate from massive transfusion; bisphosphonates or denosumab given to a vitamin D deficient patient	25-hydroxyvitamin D, phosphate (low or normal in vitamin D deficiency, high in CKD and pseudohypoparathyroidism), renal function, magnesium
Not measured	The workup has not started	—	Send it on this episode’s bloods, before treatment, on whatever tube your laboratory requires

Correct it, grade it against both scales, and check the magnesium before the PTH

A hypocalcaemia has to be corrected before it can be graded, and the correction runs the opposite way from the one people remember. About 40% of total serum calcium is bound to albumin and takes no part in the ionised fraction that tissues respond to. In hypercalcaemia, a low albumin hides a high calcium. In hypocalcaemia, a low albumin creates a low total calcium that is not physiologically low at all — the commonest cause of a total calcium below the reference interval in a hospital population is simply a low albumin. So an uncorrected total calcium in a sick patient overstates the hypocalcaemia, and treating it with intravenous calcium treats an arithmetic artefact. The albumin-corrected calcium calculator does the adjustment and sets out where the formula itself fails, which is in critical illness, chronic kidney disease and after major surgery — precisely the patients in whom the question arises. Where the answer will change management, measure an ionised calcium: the correction “is not a completely precise method, and serum ionized calcium measurements can confirm whether true hypocalcemia is present”. One warning about that sample, because it is fragile in a specific direction: delay or air exposure lets carbon dioxide escape, the pH rises, calcium binds to albumin, and the measured ionised calcium falls spuriously. A falsely low ionised calcium is the sampling error you will meet; a normal one is fairly robust.

Then grade it, and there are two published scales rather than one. The Society for Endocrinology’s emergency guidance defines severe hypocalcaemia as “Serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range”, and two independent NHS guidelines use the identical cut with mild as 1.90 to 2.19 mmol/L and asymptomatic. StatPearls, working in US units, puts severe at below 7 mg/dL, which is 1.75 mmol/L, and gives a normal total calcium of 8.5 to 10.5 mg/dL (2.12 to 2.62 mmol/L). The two severe thresholds are 0.15 mmol/L apart, so a calcium of 1.80 mmol/L is severe on one scale and not on the other. This page uses the UK cut because it is the more cautious and because of its second clause, which the US source has no equivalent of.

That second clause carries most of the clinical weight. Symptoms track the rate of fall at least as much as the absolute value. Presentation “depends on the rate of onset and chronicity of hypocalcemia”, tetany “typically occurs with a rapid decline in serum ionized calcium”, and the level at which symptoms appear “varies depending on how quickly levels fall”. A patient whose calcium has dropped to 1.95 mmol/L overnight after a thyroidectomy can be in tetany, while someone who has lived at 1.80 mmol/L for years walks about unbothered. The most useful single investigation is therefore a previous calcium, and a symptomatic patient anywhere below the reference range is treated as severe regardless of where the number sits.

The two signs everyone is taught deserve honesty. Trousseau’s sign — carpopedal spasm after a cuff is inflated 20 mmHg above systolic for two to three minutes — has a reported sensitivity of 94% and specificity of 99%, with a positive sign in only 1% to 4% of healthy people. It is worth eliciting. Chvostek’s sign is not in the same class: a positive sign “can be elicited in 25% of healthy individuals”, “29% of those with hypocalcemia did not produce a positive sign”, and a population-based study found that for every 1 mg/dL increase in calcium there was a 4% higher chance of a positive sign — the association points the wrong way. Its own reference chapter concludes that the link “has long been accepted in the medical community, despite very little literature supporting this claim”. The finding that actually tells you this is dangerous is on the ECG: QT prolongation from lengthening of the ST segment is “fairly common in hypocalcemic patients” and may predispose to torsades de pointes. Get a 12-lead ECG; do not let a negative Chvostek’s sign reassure you.

Then the workup, and it has two forks rather than one. The PTH is the famous fork: a normal gland raises PTH when calcium falls, so a PTH that is merely within the reference interval alongside hypocalcaemia is inappropriately normal and counts as low. Low or inappropriately normal means the gland — post-surgical hypoparathyroidism above all, then autoimmune, infiltrative, genetic. Raised means the gland is working and the problem is downstream — vitamin D deficiency first, then malabsorption, chronic kidney disease, pseudohypoparathyroidism, pancreatitis, tumour lysis, rhabdomyolysis, citrate. Send a 25-hydroxyvitamin D with it; the vitamin D status interpreter covers why its thresholds are contested, and the PTH converter why a PTH cannot travel between laboratories.

The fork that comes first, though, is the magnesium, and this page puts it above the PTH deliberately. Hypomagnesaemia causes a functional hypoparathyroidism, and the calcium will not correct until the magnesium does. The statement is unqualified in the literature: “It is essential to measure serum magnesium in any patient who is hypocalcemic, as correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal.” Low magnesium produces end-organ resistance to PTH and, when severe, impairs PTH secretion as well, so the whole axis is disconnected — which has a second consequence people miss: while the magnesium is low, the PTH result cannot be interpreted. A low or inappropriately normal PTH in a hypomagnesaemic patient is functional and reversible, and diagnosing hypoparathyroidism on it is a mistake. Replace both together, stop the cause — proton pump inhibitors, loop and thiazide diuretics, aminoglycosides, alcohol excess, malabsorption, chronic diarrhoea — and expect a lag, because “hypocalcemia may not be corrected for 3-7 days” after repletion begins: magnesium is predominantly intracellular and cellular uptake is slow, so a normal serum magnesium does not mean the deficit is filled. Magnesium excess does the same thing, which matters wherever magnesium sulphate is used. The magnesium unit converter handles mmol/L, mg/dL and mEq/L, which is where a surprising amount of the confusion starts. And for the opposite problem, the hypercalcaemia severity classifier is the mirror of this page.

Frequently asked questions

What calcium level counts as severe hypocalcaemia?

On UK guidance, an albumin-corrected calcium below 1.90 mmol/L (7.6 mg/dL) — and, just as importantly, symptomatic hypocalcaemia at any level below the reference range. The Society for Endocrinology’s emergency guidance defines severe as “Serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range”, and NHS Greater Glasgow and Clyde and York and Scarborough both use the same cut with mild as 1.90 to 2.19 mmol/L and asymptomatic. US sources put the threshold lower, at under 7 mg/dL (1.75 mmol/L), so a calcium of 1.80 mmol/L is severe on one scale and not on the other. This page uses the UK cut because it is more cautious and because it captures symptomatic patients whose number looks mild.

Why does my calcium not come up despite replacement?

The commonest reversible answer is magnesium. Hypomagnesaemia causes a functional hypoparathyroidism — resistance to PTH at the tissues and, when severe, impaired PTH secretion — and the standard statement is that “correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal”. Even after replacement starts, “hypocalcemia may not be corrected for 3-7 days”, because magnesium is predominantly an intracellular cation and cellular uptake is slow, so a serum magnesium that has normalised does not mean the deficit is filled. Look for the cause too: proton pump inhibitors, loop and thiazide diuretics, aminoglycosides, alcohol excess, malabsorption and chronic diarrhoea. Vitamin D deficiency and untreated hypoparathyroidism are the other reasons replacement underperforms.

How reliable are Chvostek’s and Trousseau’s signs?

They are not equivalent. Trousseau’s sign — carpopedal spasm after inflating a cuff 20 mmHg above systolic for two to three minutes — has a reported sensitivity of 94% and specificity of 99%, with a positive sign in only 1% to 4% of healthy people, and is worth eliciting. Chvostek’s sign is much weaker: a positive sign can be elicited in 25% of healthy individuals, 29% of hypocalcaemic patients do not produce one, and a population-based study found a positive sign became more likely as calcium rose, by about 4% per mg/dL. Its own reference chapter concludes that the association with hypocalcaemia has been accepted “despite very little literature supporting this claim”. Diagnose on the corrected calcium and get a 12-lead ECG for QT prolongation.

What ECG change does hypocalcaemia cause?

QT prolongation, produced by lengthening of the ST segment rather than by a change in the T wave itself. It is “fairly common in hypocalcemic patients” and matters because a prolonged QTc may predispose to torsades de pointes. A 12-lead ECG belongs in the initial assessment of any significant hypocalcaemia, and ECG monitoring is part of the published treatment: intravenous calcium gluconate is given “over 10 min with ECG monitoring” and repeated until the patient is asymptomatic.

Should calcium be corrected for albumin before grading a hypocalcaemia?

Yes, and the reason is the opposite of the one that applies in hypercalcaemia. About 40% of total calcium is albumin-bound and inactive, so a low albumin lowers the measured total calcium without lowering the ionised fraction — it creates a hypocalcaemia that is not physiologically real. In a hospital population, low albumin is the commonest reason for a total calcium below the reference interval, so grading an uncorrected value overstates the severity and can lead to treating an artefact. Use the corrected calcium calculator, and measure an ionised calcium where the answer will change management, because the correction formula is unreliable in critical illness, chronic kidney disease and after major surgery.

What is the first test in a hypocalcaemia workup?

PTH and magnesium, on the same request, before treatment starts. The PTH is the classical branch point: low or inappropriately within the reference range means the parathyroid gland is the problem, with post-surgical hypoparathyroidism much the commonest; raised means the gland is responding correctly and the problem is downstream, with vitamin D deficiency at the top of that list. The magnesium comes with it because hypomagnesaemia mimics hypoparathyroidism exactly — it causes a functional, fully reversible PTH deficiency and resistance — so a low PTH cannot be interpreted until the magnesium is known. Send phosphate, renal function and a 25-hydroxyvitamin D alongside them.

Can someone have symptoms of hypocalcaemia with a normal calcium?

Yes, and the classical example is acute hyperventilation. Respiratory alkalosis raises the pH, which drives calcium onto albumin and lowers the ionised fraction while the total calcium stays completely normal — producing perioral and peripheral paraesthesiae and carpopedal spasm in someone whose calcium result is unremarkable. It needs no calcium replacement. The converse also happens: acidosis displaces calcium from albumin and raises the ionised fraction, which can mask a real hypocalcaemia on an ionised measurement taken during acidaemia.

Related calculators

References

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. Severe hypocalcaemia as “Serum calcium <1.9 mmol/L and/or symptomatic at any level below reference range”; treatment “Initially, give 10–20 mL 10% calcium gluconate in 50–100 mL of 5% dextrose i.v. over 10 min with ECG monitoring. This can be repeated until the patient is asymptomatic”, followed by a diluted calcium gluconate infusion titrated to achieve normocalcaemia.
NHS Greater Glasgow and Clyde. Management of Hypocalcaemia. Mild hypocalcaemia as “serum adjusted calcium 1.9-2.2mmol/L and asymptomatic” and severe as “serum adjusted calcium <1.9mmol/L and/or symptomatic”; symptoms typically below 1.9 mmol/L “though the threshold varies depending on how quickly levels fall”; a 12-lead ECG for QT prolongation; intravenous magnesium where the patient is hypomagnesaemic.
York and Scarborough Teaching Hospitals NHS Foundation Trust. Investigation of Hypocalcaemia in Primary Care (Adults). “Mild Hypocalcaemia = 1.90 – 2.19 mmol/L, asymptomatic”; “Severe Hypocalcaemia = <1.90 mmol/L and / or symptomatic at any level below reference range”; the initial panel of albumin-adjusted calcium, PTH on a separate EDTA sample, magnesium, urea and electrolytes, vitamin D and phosphate; hypomagnesaemia listed as a cause of inadequate PTH.
Schafer AL, Shoback DM. Hypocalcemia: Diagnosis and Treatment. In: Endotext. South Dartmouth (MA): MDText.com; NCBI Bookshelf NBK279022. “It is essential to measure serum magnesium in any patient who is hypocalcemic, as correction of hypomagnesemia must occur to overcome PTH resistance before serum calcium will return to normal”; even after repletion begins “hypocalcemia may not be corrected for 3-7 days. This may be because cellular uptake of magnesium is slow, and magnesium is predominantly an intracellular cation”; magnesium excess as well as deficiency listed under functional hypoparathyroidism; “Prolongation of the QT-interval due to lengthening of the ST-segment on electrocardiogram is fairly common in hypocalcemic patients”; “Chvostek’s sign is also present in 10% of normal individuals”; and that albumin correction “is not a completely precise method, and serum ionized calcium measurements can confirm whether true hypocalcemia is present”.
Anastasopoulou C, Goyal A. Hypocalcemia. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 8 June 2026. NCBI Bookshelf NBK430912. Normal total serum calcium “8.5 to 10.5 mg/dL (2.12-2.62 mmol/L)” and ionised “4.65 to 5.25 mg/dL (1.16-1.31 mmol/L)”; severe hypocalcaemia “<7 mg/dL”; “Presentation also depends on the rate of onset and chronicity of hypocalcemia” and tetany “typically occurs with a rapid decline in serum ionized calcium”; “Low serum magnesium induces PTH resistance and, in some severe cases (typically <0.8 mEq/L), impairs PTH secretion”; QTc prolongation that “may predispose to torsades de pointes”.
Patel M, McMahon K, Hu EW. Trousseau Sign. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 23 June 2025. NCBI Bookshelf NBK557832. “the sensitivity and specificity of the Trousseau sign in hypocalcemia are reported to be 94% and 99%, respectively”; a positive sign in “up to 1% to 4% of healthy individuals without hypocalcemia”; elicited by inflating a cuff 20 mmHg above systolic for 2 to 3 minutes.
Omerovic S, Das JM. Chvostek Sign. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 1 May 2023. NCBI Bookshelf NBK542326. “a positive Chvostek sign can be elicited in 25% of healthy individuals”; “29% of those with hypocalcemia did not produce a positive sign”; Hujoel’s population-based finding that “for every 1 mg/dl increase in calcium, there was a 4% higher chance of a positive Chvostek sign”; and “The correlation between hypocalcemia and the Chvostek sign has long been accepted in the medical community, despite very little literature supporting this claim”.
International Union of Pure and Applied Chemistry. Standard atomic weight of calcium, 40.078 — the basis for the mmol/L to mg/dL factor of 4.0078 used throughout this page, and the same factor used by the site’s hypercalcaemia severity classifier so that the two pages agree.

Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.