Quick tip - 40-45% of calcium circulates bound to albumin, so disorders of albumin can cause apparent (false) hypo or hypercalcaemia – calcium levels should therefore always be adjusted for albumin concentration.
Serum calcium is regulated by parathyroid hormone (PTH) and vitamin D (dependent on sufficient dietary intake).
High serum calcium is usually (~90% of the time) caused by primary hyperparathyroidism (PTH excess) or malignancy.
Symptoms depending on the degree of hypercalcaemia, and include polyuria and thirst, constipation, bony pains, weakness and (less commonly) delirium. Hypercalcaemia in the long term is associated with renal stones and osteoporosis.
-Mild hypercalcaemia picked up incidentally on routine blood testing usually suggests chronic hyperparathyroidism
-Short history with severe symptoms and marked hypercalcaemia suggests malignancy (usually otherwise obvious)
Causes of hypercalcaemia:
Useful to stratify as:
PTH dependent (PTH inappropriately high or mid-high normal when calcium is high)
PTH independent (PTH appropriately suppressed or low-normal when calcium is high)
Quick tip – ensure vitamin D is well replaced before giving parenteral bisphosphonates or denosumab for osteoporosis, and before head and neck surgery, to avoid crashing into hypocalcaemia
Serum calcium levels are controlled by parathyroid hormone (PTH) and vitamin D, as well as by calcium and phosphate status.
Hypocalcaemia can therefore be caused by:
Calcium circulates bound to albumin, so we adjust total calcium levels for albumin. In cases of acid-base disturbance, calcium binding to albumin may be affected so an ionised calcium may be more accurate but is rarely indicated.
Causes of hypocalcaemia:
Like hypercalcaemia, it is useful to consider PTH dependent and independent causes. The usual response to hypocalcaemia would be a rise in PTH – if this does not occur it suggests a parathyroid problem.
PTH low or normal – primary hypoparathyroidism
Symptoms and signs:
Causes may be clinically obvious e.g. post thyroid surgery. In patients with vitamin D or PTH resistance there is usually childhood onset and a family history.
SOCIETY FOR ENDOCRINOLOGY ENDOCRINE EMERGENCY GUIDANCE: Emergency management of acute hypocalcaemia in adult patients. (2016) URL: https://ec.bioscientifica.com/view/journals/ec/5/5/G7.xml
NICE Clinical Knowledge Summaries. Vitamin D in adults – treatment and prevention. URL: https://cks.nice.org.uk/vitamin-d-deficiency-in-adults-treatment-and-prevention#!scenario