- Normal serum corrected calcium = 2.1 – 2.6 mmol/L
- Mild hypercalcaemia = 2.7 – 2.9 mmol/L
- Moderate hypercalcaemia = 3.0 – 3.4 mmol/L
- Severe hypercalcaemia = greater than 3.4 mmol/L
- primary hyperparathyroidism (most commonly due to a benign parathyroid adenoma)
- familial hypocalciuric hypercalcaemia
- sudden acidosis (resulting in release of bound calcium)
- chronic renal failure
- Addison’s disease
- ingestion of excess calcium (milk-alkali syndrome) or vitamin D
- drugs e.g. lithium, thiazide diuretics, theophylline toxicity
- prolonged immobilisation
- bone destruction usually by secondary deposits from malignancy or myeloma
The commonest causes of hypercalcaemia are primary hyperparathyroidism and hypercalcaemia of malignancy.
- STONES (renal calculi)
- BONES (bone pain, fragile bones)
- GROANS (lethargy, fatigue, generalised muscle weakness)
- MOANS (constipation, abdominal pain, nausea/vomiting, pancreatitis, peptic ulcer)
- THRONES (polyuria, polydipsia, dehydration, renal failure)
- PSYCHIATRIC OVERTONES (confusion, depression, anxiety, hallucinations, insomnia)
- The most common ECG abnormality is shortening of the QT interval
- In severe hypercalcaemia, Osborn waves (J waves) may be seen
- Ventricular irritability and VF arrest has been reported with extreme hypercalcaemia
- Normal serum corrected calcium = 2.2 – 2.6 mmol/L
- Mild-moderate hypocalcaemia = 1.9 – 2.2 mmol/L
- Severe hypocalcaemia = < 1.9 mmol/L
- Hypoparathyroidism (e.g. DiGeorge syndrome, autoimmune, secondary to parathyroid or thyroid surgery, radiation or chemotoxic agents, infiltrative disease of the parathyroid glands or hypomagnesaemia) or pseudohypoparathyroidism (characterised by target organ resistance to PTH)
- Acute pancreatitis
- Renal failure
- Vitamin D deficiency
- Alkalosis or massive blood transfusion (due to increased intravascular ionised calcium binding)
- Rhabdomyolysis or tumour lysis syndrome (due to extravascular calcium deposit)
- Drugs e.g. bisphosphonates, fluoride poisoning, combination chemotherapy
- Sepsis (due to impaired secretion of calcitriol and PTH, target organ resistance to PTH and increased lactate binding calcium in serum).
The most common causes are hypoparathyroidism (frequently following surgery), vitamin D deficiency or abnormal vitamin D metabolism, chronic kidney disease and hypomagnesaemia.
Patients with adjusted serum calcium > 1.9 are usually asymptomatic but many patients become symptomatic when levels are less than this.
Features of hypocalcaemia include:
- carpopedal spasm in response to inflating a blood pressure cuff to above systolic BP (Trousseau’s sign)
- twitching of the ipsilateral facial muscles in response to tapping on the facial nerve (Chvostek’s sign)
- painful and fragile bones
- numbness and paraesthesia in hands and feet
- muscle cramps and spasms
- cardiac arrhythmias
- cardiac failure
- prolonged QT interval
- mood changes
- Hypocalcaemia causes QTc prolongation primarily by prolonging the ST segment.
- The T wave is typically left unchanged.