Definition and epidemiology
Hypocalcemia is a corrected total serum calcium or an ionised calcium below the age-specific reference range. Practical thresholds: total serum calcium <8 mg/dL (2.0 mmol/L) or ionised calcium <4.4 mg/dL (1.1 mmol/L) in term infants and children; for very-low-birth-weight infants <1500 g, total <7 mg/dL (1.75 mmol/L) or ionised <4 mg/dL (1.0 mmol/L). Ionised calcium is the physiologically active fraction and the most reliable measure, particularly with altered albumin or acid–base status. Always correct total calcium for albumin (add ~0.8 mg/dL per 1 g/dL fall below 4 g/dL). Neonatal hypocalcemia divides into early (<72 h: prematurity, maternal diabetes, perinatal asphyxia, IUGR) and late (>72 h: high phosphate load, hypomagnesaemia, maternal/infant vitamin D deficiency — common in India, hypoparathyroidism). Beyond the neonatal period, vitamin D deficiency, hypoparathyroidism, renal disease and hypomagnesaemia predominate.
Clinical features
Severity reflects the absolute level and rate of fall. Increased neuromuscular excitability produces perioral and acral paraesthesiae, muscle cramps, carpopedal spasm, tetany, laryngospasm/stridor, and seizures. Elicit Chvostek sign (facial twitch on tapping the facial nerve anterior to the ear) and Trousseau sign (carpopedal spasm after cuff inflation above systolic pressure for 3 minutes) — though both are less reliable in neonates. Neonates show non-specific signs: jitteriness, irritability, poor feeding, hypotonia, apnoea, tachypnoea and seizures. Chronic hypocalcemia may cause cataracts, dental enamel defects and basal ganglia calcification.
Diagnosis
Confirm with ionised (or albumin-corrected total) calcium, then work up the cause: phosphate, magnesium, alkaline phosphatase, PTH, 25-OH vitamin D, renal function and urine calcium/creatinine. Crucially, check magnesium — hypomagnesaemia causes refractory hypocalcemia that will not correct until magnesium is replaced. Obtain an ECG: hypocalcemia prolongs the QTc and predisposes to arrhythmia. Interpret PTH against the calcium (low/inappropriately normal PTH = hypoparathyroidism; high PTH = vitamin D deficiency or resistance/pseudohypoparathyroidism).
See the full criteria: Hypocalcemia
Red flags
- Tetany, laryngospasm/stridor, or seizures — symptomatic hypocalcemia needing urgent IV calcium
- Prolonged QTc, arrhythmia, or signs of reduced cardiac output
- Coexisting hyperphosphataemia (tumour lysis, renal failure, phosphate enema)
- Hypomagnesaemia — calcium will not correct until magnesium is replaced
- Stridor or apnoea in a neonate; suspected DiGeorge (22q11) with conotruncal cardiac disease
Management overview
Symptomatic or severe hypocalcemia (tetany, seizures, laryngospasm, QTc prolongation) requires IV calcium (calcium gluconate preferred peripherally) given slowly with continuous cardiac monitoring — extravasation causes severe tissue necrosis and rapid infusion causes bradycardia/arrest. Correct magnesium concurrently if low, or calcium replacement fails. Asymptomatic or chronic hypocalcemia is managed with oral calcium and activated vitamin D (calcitriol/alfacalciferol where 1-hydroxylation is impaired, e.g. hypoparathyroidism or renal disease) plus treatment of the underlying cause — vitamin D and phosphate-binding strategies as appropriate. Recheck calcium, phosphate and magnesium during correction; in hypoparathyroidism aim for low-normal calcium to limit hypercalciuria and nephrocalcinosis. (Doses are intentionally omitted — follow your local formulary.)
References
- Vuralli D. Int J Pediatr. 2019;2019:4318075 (hypocalcemia in newborn and infancy).
- Schafer AL, Shoback DM. Hypocalcemia: Diagnosis and Treatment. Endotext, 2023.
- Nelson Textbook of Pediatrics, 21st ed.
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.