Hypocalcaemia and hypoparathyroidism

Hypoparathyroidism (HPTH) refers to underactivity or complete loss of the parathyroid glands. This most commonly arises following neck surgery, but congenital, auto-immune and genetic causes are also seen. The diagnosis is confirmed biochemically with hypocalcaemia, hyperphosphataemia and low parathyroid hormone levels.

Emergency management of hypocalcaemia

Patients with symptoms of tetany, with a positive Trousseau sign, or in whom calcium is falling rapidly post operatively, or whose serum calcium is <1.8mmol/L usually require intravenous calcium gluconate supplementation.

Administer (1.7x patient's weight in kg) mls 10% calcium gluconate in 1l 0.9%saline over a 4 hour infusion. This standardised dose can be administered repeatedly until corrected calcium is >1.8ml/l. 

Recheck serum calcium  one hour post infusion, then at least 12 hourly for 24 hours, then daily. 

Also check the patient's serum magnesium level and replace as necessary. 

In patients post neck surgery, if levels do not stabilise, start oral calcium supplements (e.g. Sandocal TM 2 tablets twice daily), and check serum PTH to risk stratify the patient.

Repeated doses of intravenous calcium may be necessary, and 1 alpha-calcidol should also be started for prolonged hypocalcaemia or a serum PTH <0.6pmol/l.

See emergency treatment of post operative hypocalcaemia for more details on how to treat and prevent this complication. 

Activated Vitamin D analogs

PTH is required for the activation of vitamin D to the hormone calcitriol (1,25-hydroxy vitamin D). Since PTH treatment is not readily available, treatment of HPTH is based on treatment with activated vitamin D. Alphacalcidol is 1 alpha-hydroxylated and requires 25 alpha-hydroxylation in the liver to form calcitriol.

This is the most commonly prescribed treatment in the UK. Calcitriol (brand named rocaltrol) is 1,25 hydroxylated already, and is most widely used in the US. 

Suitable starting doses are 0.5mcg -1mcg of either agent, though doses are adjusted to maintain a low normal serum calcium level, with withdrawal of calcium supplements in most cases.

Vitamin D3 supplements which can be bought over the counter, are not activated and are prescribed for vitamin D deficiency not for HPTH.

Calcium supplements  

Calcium supplementation (e.g. 1200-2000mg/day) is necessary at the time of diagnosis, when patients are symptomatically hypocalcaemic and for emergency treatment.

However, these can be unpleasant to take, and in many cases become unnecessary as adequate doses of 1alpha-calcidol increase gastrointestinal absorption of dietary calcium. Conversely, low dose calcium supplementation if tolerated, can reduce the 1alpha-calcidol dose required, and paradoxically reduce urinary calcium excretion and hence the risk of renal complications.

Magnesium supplements

These are not necessary routinely, but may help patients tolerate lower calcium levels.

Vitamin D3

Although the major actions of vitamin D require PTH dependent 1alpha-hydroxylation, some PTH independant conversion occurs locally e.g. within immune tissues.

These non-endocrine effects are not well understood, but many patients report improved stability of their hypocalcaemia and general condition after correction of low vitamin D levels.

Dietary advice

A very high calcium diet is not necessary though a good intake of calcium, magnesium and vitamin D3 may enable patients to tolerate lower serum calcium levels.

Patient education

All patients with HPTH are at risk of hypocalcaemic crises although these are rare. Patients require education about the importance of taking their medication regularly and the need for regular blood testing.

Patient also need to recognise the warning symptoms of hypocalceamia, understand how their diet may perfect their calcium levels, and need to know how best to access medical care in emergency situations.

Emergency identification may be useful particularly for people with difficult to control hypocalceamia.

Genetic counselling

All affected families should be offered genetic counselling and screening where appropriate.