Hypocalcaemia
Background Information
Definition
Hypocalcaemia is defined as serum adjusted calcium <2.20 mmol/L
- Severe hypocalcaemia: serum adjusted calcium <1.90 mmol/L
- Note the lower limit for ionised calcium is 1.15 mmol/L
Adjusted calcium takes serum albumin into account, it estimates true calcium level when albumin is abnormal.
Ionised calcium directly measures the biologically active form of calcium. This is the best marker of calcium status, typically used when accuracy is critical (e.g. critical illness, acid-base disorders)
Aetiology
Key causes:
| Hypoparathyroidism – common | Most commonly from surgery (parathyroidectomy / thyroidectomy)
See the Hypoparathyroidism article for more information |
| Hypomagnesaemia | Hypomagnesaemia reduces PTH secretion (magnesium is required for PTH release) and causes PTH resistance in target tissue → hypocalcaemia
*Hypomagnesaemia can cause both hypocalcaemia and hypokalaemia |
| Vitamin D deficiency – common | E.g. CKD, malnutrition, malabsorption, lack of sunlight exposure, dietary insufficiency
See the Vitamin D Deficiency article for more information |
| Calcium complex formation | Severe acute pancreatitis can cause hypocalcaemia
Rhabdomyolysis and tumour lysis syndrome
Blood transfusion (esp. massive transfusion)
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| Drugs |
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| Hyperventilation | Hyperventilation → respiratory alkalosis → more ionised calcium bind albumin → less free ionised calcium |
Clinical Features
| Early / mild hypocalcaemia features [Ref] |
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| Features of more severe hypocalcaemia: [Ref] |
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Hypocalcaemia increases neuromuscular excitability because ionised calcium normally stabilises voltage-gated sodium channels. When calcium levels fall, these channels open more easily, leading to spontaneous depolarisation.
Investigation and diagnosis
Initial biochemical investigations: [Ref]
- Serum adjusted calcium and phosphate
- Vitamin D
- PTH
- Magnesium
- U&E
It is important to check magnesium levels when treating hypocalcaemia (and hypokalaemia!). If it is secondary to hypomagnesaemia, the hypocalcaemia (or hypokalaemia) will NOT correct until magnesium is replaced, regardless of how much calcium (or potassium) is given.
Management
Management depends on 1) the severity and 2) whether the patient is symptomatic or not.
Mild Hypocalcaemia (1.9-2.2 mmol/L) and Asymptomatic
Treat with oral calcium supplement (e.g. Calcichew Forte chewable) [Ref]
- Consider vitamin D supplementation if there is evidence of vitamin D deficiency
If the patient also has magnesium deficiency → correct hypomagnesaemia first and reassess (this might be enough to correct the hypocalcaemia)
Severe Hypocalcaemia (<1.9 mmol/L) or Symptomatic
Initial management: IV calcium gluconate 10% [Ref]
- ECG monitoring is necessary
- Followed by a continuous IV infusion of calcium gluconate later on
If the patient also has magnesium deficiency → give IV calcium urgently and also give IV magnesium promptly.