Investigation of Investigation of Hypercalcaemia (High Calcium)

Is it artefact?

Serum calcium concentration is often falsely raised because:

• fasting specimens are not collected
• of prolonged use of tourniquet

Calcium concentrations rise after a meal but the reference range is based on fasting blood collections.

Is it drug-related?

Drugs to consider include thiazide diuretics and lithium, which affect renal handling.

Disease

A calcium concentration of greater than 3.0 mmol/L is cause for concern.

Primary hyperparathyroidism is the most common cause of hypercalcaemia outside the hospital setting. It is also an important cause of hypercalcaemia in the young. The autonomous nature of parathyroid hormone (PTH) secretion is revealed by the positive correlation between the serum (ionised) calcium and the serum PTH. In normal subjects they are inversely related.

The most common cause of hypercalcaemia is malignancy, which accounts for approximately 50% of cases. It is frequently accompanied by a low albumin level.

Malignant causes may include:

• bone metastases with osteolytic deposits e.g. breast cancer
• tumour production of parathyroid related peptide (PTHrP)

In malignancy, parathyroid hormone (PTH) is suppressed, whereas in primary hyperparathyroidism it is usually, but not always, raised.

Rarer causes of hypercalcaemia may include sarcoidosis where serum 1,25-dihydroxyvitamin D levels are raised, vitamin D toxicity and familial hypocalciuric hypercalcaemia where there is an inactivating mutation of the calcium sensor in the parathyroids.

 

More information: MBA - Calcium, phosphate, magnesium, cholesterol