Makindo Medical Notes

Related Subjects: |Calcium Physiology |Calcitonin |Hypocalcaemia |Hypercalcaemia |Hypomagnesaemia |Hypermagnesaemia |Primary Hyperparathyroidism |Familial hypocalciuric hypercalcaemia (FHH) |Sarcoidosis

If you find hypocalcaemia and the cause is not obvious, always check for low magnesium, as it causes end-organ resistance to PTH and inhibits the hypocalcaemic feedback loop.

Calcium Levels: To convert from mg/dL (US) to mmol/L (UK), multiply by 0.25

Aetiology

• Hypocalcaemia increases membrane potential so that cells are more easily depolarised.
• Neuromuscular excitability with muscle contraction and cardiac arrhythmias.

Causes

Clinical: Acute

• Tetany, perioral paraesthesia, cramps, carpopedal spasms.
• Chvostek’s sign: Tapping the facial nerve causes contraction of the facial muscles.
• Trousseau’s sign: Inflation of a BP cuff > systolic for 3 minutes causes carpopedal spasm.
• Laryngeal spasm and stridor may occur.
• Severe cases can result in papilloedema.
• Seizures: all types have been reported.
• ECG changes include prolonged QT interval and arrhythmias.

Trousseau’s sign with acute hypocalcaemia

Clinical: Chronic

• Poor dentition, seizures, neuromuscular irritability.
• Dry skin, coarse hair, brittle nails, psoriasis, chronic pruritus.
• Calcification of basal ganglia with extrapyramidal signs.
• Calcification of the cerebellum and cerebrum may occur.
• Papilloedema, subcapsular cataracts.
• Psychiatric manifestations such as depression or psychosis.

Investigations

• U&E: Renal function, corrected calcium, albumin, phosphate, magnesium.
• iPTH: the single most important diagnostic test.
• Long QT can lead to arrhythmias.
• Vitamin D and its metabolites.
• ECG: Prolonged QT interval and possible arrhythmias.

Low Calcium and High PTH

• Chronic kidney disease: Low Ca, High P, High ALP, and High PTH.
• Vitamin D deficiency: Low Ca, Low P, High ALP, and High PTH.
• Pseudohypoparathyroidism.
• Hypomagnesaemia (consider PPI-associated hypomagnesaemia).
• Rhabdomyolysis (initially).
• High phosphate.
• Acute respiratory alkalosis (increased albumin binding causes a relative fall in free ionised calcium).
• Acute pancreatitis (free fatty acids chelate calcium).
• Drugs: cisplatin, bisphosphonates, phenytoin, rifampicin.
• Citrate following large transfusion.

Low Calcium and Low PTH

• Hypoparathyroidism: serum calcium is low, phosphate is high.
• Hypoparathyroidism can be congenital, autoimmune, or occur after thyroid/parathyroid surgery.
• Hypomagnesaemia (consider PPI-associated hypomagnesaemia).

Management

• Mild hypocalcaemia (1.9–2.13 mmol/L): Use oral supplements of calcium. Vitamin D or magnesium may be needed depending on the cause. Monitor serum calcium levels weekly, then every 3–6 months once stable. Titrate calcium dose according to levels. For example, Sandocal 1000, two tablets BD (alternatives: Adcal three tablets BD, Cacit four tablets BD, or Calcichew Forte two tablets BD).
• Severe hypocalcaemia (e.g., tetany or < 1.9 mmol/L):
  • ABC, manage seizures, arrhythmias.
  • Give 10 ml of 10% calcium gluconate in 100 ml of 0.9% saline or 5% dextrose over 10–20 minutes (depending on urgency). In an emergency (e.g., tetany), it can be given neat by slow IV injection over at least 3 minutes with ECG monitoring.
  • Monitor serum calcium levels (check about 2 hours post-dose) and repeat if necessary.
  • If the patient remains symptomatic, an infusion is often needed to prevent recurrence. For example, 100 ml of 10% calcium gluconate in 1000 ml of 0.9% saline or 5% dextrose at 50 ml/hr, adjusting the rate per response. Monitor serum calcium 4–6 hourly.
• Continuing hypocalcaemia can be managed with oral calcium and vitamin D and treatment of the underlying cause.
• Note: Calcium is highly irritant. Administer via a small needle into a large vein to avoid extravasation. Rapid administration can cause flushing, hypotension, bradycardia, arrhythmias, and cardiac arrest.
• Caution in digoxin use: Calcium enhances digoxin’s cardiac effects and may precipitate digitalis toxicity.
• Oral calcium can cause diarrhoea or constipation, nausea, and gastric pain. It also impairs the absorption of other medications (e.g., tetracyclines, iron, bisphosphonates). Leave an interval of at least three hours between calcium and these medications.
• Calcium chloride is an alternative to calcium gluconate but is more irritant and should only be given via a central line.

References

• Hypocalcaemia NHS Guidance
• Leicester NHS Guidelines