4th April 2024

Hypocalcaemia

This is defined as calcium levels <2.20mmol/mol in the presence of normal serum plasma protein concentrations. It is crucial to check serum albumin levels and adjust accordingly, as over 40% of circulating calcium is bound to albumin. 

Both the absolute level and rate of the fall in adjusted serum calcium levels are important, with symptoms typically developing if AdjCa ≤1.9mmol/L or if there is a rapid decrease. 

Measuring PTH level is crucial to identifying the cause of hypocalcaemia. Causes of hypocalcaemia with a low PTH have been previously described in the hypoparathyroidism section.  Causes of hypocalcaemia with high PTH include:

• Vitamin D deficiency/chronic kidney disease: resulting in secondary hyperparathyroidism
• Pseudohypoparathyroidism, where impaired PTH response results in renal calcium excretion  
• Acute pancreatitis: hypocalcaemia due to calcium saponification 
• Sepsis and severe burns: multifactorial causes of hypocalcaemia

Complications

Severe or symptomatic hypocalcaemia may result in life-threatening complications. It characteristically causes prolonged QT interval, which can lead to life-threatening dysrhythmias such as torsades de pointes and ventricular fibrillation. 

Management 

Treatment of severe or symptomatic hypocalcaemia is a medical emergency, managed with 10% calcium gluconate, with repeated doses given until a patient is asymptomatic, or calcium level has normalised. Chronic, or mild/asymptomatic hypocalcaemia can be managed with oral calcium and vitamin D supplements.

Care must be exercised as overzealous calcium replacement, particularly when given via the intravenous route, can also lead to serious arrhythmias.