Hypocalcemia
Defined as ionized serum calcium <4.65mg/dL (<1.16mmol/L) and a total serum calcium <8.5mg/dL (<2.12 mmol/L). We generally classify hypocalcemia based on if the PTH concentrations are low (i.e. hypoparathyroid disorders) or high (i.e. secondary hyperparathyroidism). Most commonly, hypocalcemia is caused by hypoparathyroidism, a deficiency of vitamin D, acute or chronic renal failure or hypomagnesemia.
Again, the symptoms of hypocalcemia can be varied, from life-threatening to asymptomatic. At the most severe scale are symptoms associated with neuromuscular irritability and ectopic calcification (e.g. in the basal ganglia which can cause extrapyramidal neurological symptoms). Clinical features include:
- Paresthesia (fingers, toes)
- Tetany
- Chvostek’s sign
- Twitching of the facial muscles when taping of zygomatic bone
- Trousseau's sign
- Carpopedal spasm caused by inflating blood-pressure cuff
- Seizures
- Prolonged QT
- Laryngospasm
- Bronchospasm
ECG in hypocalcaemia: prolonged QT interval (long ST segment).
Image: “ECG Hypocalcemia” by Ewingdo, CC BY-SA 4.0, via Wikimedia Commons.
Image: “Trousseau's Sign of Latent Tetany” by Tmdswan, CC BY-SA 4.0, via Wikimedia Commons.
Use the flowchart below to help guidance
In hypoparathyroidism, serum calcium is low, phosphate is high, and PTH is undetectable.
Management of acute hypocalcemia is calcium gluconate, 10mL 10% w/v IV, diluted in 50mL of 5% dextrose or 0.9% NaCl in slow injection This can be repeated as required. If hypocalcemia is chronic, oral vitamin D therapy (active vitamin D, e.g. calcitriol, in hypoparathyroidism) should also be administered with exogenous oral calcium.