FFinalistSouthampton · 2027
Endocrine
AKT · Endocrine/Calcium, bone & parathyroidlow yield

Hypocalcaemia

Low calcium (vitamin D deficiency, hypoparathyroidism, CKD, hypomagnesaemia)

Overview

Low corrected calcium, causing neuromuscular irritability. Causes split by PTH/phosphate: vitamin D deficiency and CKD (HIGH PTH = secondary hyperparathyroidism), hypoparathyroidism (LOW PTH, high phosphate), hypomagnesaemia, acute pancreatitis, and rhabdomyolysis/tumour lysis. Treated with calcium and (active) vitamin D; IV calcium if severe.

Recognise

  • Paraesthesiae (perioral, fingers), cramps, carpopedal spasm, TETANY; Chvostek and Trousseau signs
  • Severe: laryngospasm, seizures, prolonged QT/arrhythmia
  • Phosphate and PTH localise the cause

Red flags

  • Tetany, seizures, laryngospasm, long QT → IV calcium gluconate
  • Severe hypocalcaemia after thyroid/parathyroid surgery, or in tumour lysis/rhabdomyolysis

Differentials & how to tell them apart

Vitamin D deficiency / CKDhigh PTH (secondary hyperparathyroidism); CKD also has high phosphate
HypoparathyroidismLOW PTH with HIGH phosphate (post-surgical/autoimmune)
Hypomagnesaemialow magnesium — correct it first or calcium won't respond
Acute pancreatitis / tumour lysis / rhabdomyolysiscalcium sequestration in the relevant acute context

Investigations

Corrected calcium, phosphate, PTH, magnesium, vitamin D, renal function; ECG (long QT). Amylase/lipase if pancreatitis suspected.

Management

Calcium + vitamin D (IV calcium gluconate if severe); correct magnesium

  1. 1Severe/symptomatic → IV calcium gluconate with monitoring. Use PTH and phosphate to find the cause; correct magnesium. Replace vitamin D for deficiency.Gate: Correct hypoMAGNESAEMIA first (it causes refractory hypocalcaemia); the PTH level distinguishes vitamin D deficiency/CKD (high PTH) from hypoparathyroidism (low PTH)
  2. 2Cause-specific maintenance (colecalciferol vs active vitamin D); monitor calcium/renal function.
Oral calcium + vitamin D (or active vitamin D) — maintenance; colecalciferol for deficiency, alfacalcidol/calcitriol for hypoparathyroidism/CKD
IV calcium gluconate (severe/symptomatic) — with cardiac monitoring
Correct magnesium — essential — refractory otherwise

Key points

Tetany + Chvostek/Trousseau + long QT = hypocalcaemia. PTH/phosphate sort the cause; always check magnesium. High PTH = vitamin D/CKD; low PTH = hypoparathyroidism.

Monitor & prognosis

Calcium, magnesium, renal function, ECG.

Good once cause treated.

Source: Society for Endocrinology