Box 24.1 Causes of hypocalcaemia

Vitamin D deficiency

Lack of sun exposure

Poor intake or malabsorption (e.g. coeliac disease)

Liver failure (decreased 25-hydroxylation of vitamin D), medications increasing vitamin D metabolism, e.g. phenytoin

Chronic kidney disease

Impaired activation of vitamin D due to mutations in the 1α- hydroxylase gene (vitamin D-dependent rickets type 1)

Target organ resistance due to mutations in the vitamin D receptor gene (vitamin D-dependent rickets type 2)

Hypoparathyroidism

Post thyroid or parathyroid surgery (hypoparathyroidism may be transient or permanent)

Autoimmune, e.g. part of autoimmune polyglandular syndrome type 1 (see Chapter 6)

Infiltrative diseases of the parathyroid glands: haemochromatosis, Wilson’s disease, granulomas, metastatic cancer

Congenital: DiGeorge syndrome (defective development of the pharyngeal pouch system, resulting in cardiac defects, cleft palate and abnormal facies, hypoplastic thymus and hypoparathyroidism)

Hypomagnesaemia: due to malabsorption, chronic alcoholism, prolonged parenteral fluid administration, diuretics, aminoglycosides and cisplatin

HIV infection

Pseudohypoparathyroidism (end-organ parathyroid hormone resistance): type 1a, type 1b, type 2

Extravascular c alcium d eposition

Hungry bone syndrome

Pancreatitis

Rhabdomyolysis

Tumour lysis syndrome

Widespread osteoblastic metastases

Increased intravascular calcium binding

Respiratory alkalosis

Massive blood transfusions

Sepsis

Drugs

Combination chemotherapy with 5-fluorouracil and leucovorin (decreases calcitriol production), fluoride poisoning (inhibits bone resorption), bisphosphonates (suppress the formation and function of osteoclasts)

Calcium-sensing receptor gene mutations (autosomal dominant) or autoantibodies directed against the calcium-sensing receptor

Rarer causes of hypocalcaemia include calcium-sensing receptor gene mutations (autosomal dominant) or autoantibodies directed against the calcium-sensing receptor, resulting in hypocalcaemia and hypercalciuria.

Pseudohypocalcaemia may be seen in patients who have had some of the gadolinium-based contrast agents for magnetic resonance angiography, due to interference with the colorimetric assays for calcium.