The clinical presentation of hypocalcaemia (serum ionized calcium < 1.10 mmol/ L or albumin- adjusted calcium < 2.20 mmol/ L) relates to its severity and rapidity of onset, and may range from an asymptomatic biochemical abnormality to a life- threatening disorder. Severe hypocalcaemia (serum ionized calcium < 0.95 mmol/ L or serum albumin- adjusted calcium and toes; and also muscle cramps, carpopedal spasms, laryngospasm and bronchospasm, seizures of all types, and cardiac arrhythmias as sociated with prolongation of the QT interval on electrocardiogram (ECG). Chronic hypocalcaemia (which has occurred over a period of months to years) may be associated with subcapsular cataracts, papilloedema and abnormal dentition. Moreover, patients with chronic hypocalcaemia caused by hypoparathyroidism frequently develop ectopic mineralization. Indeed, more than 70% of patients with idiopathic hypoparathyroidism have been reported to have calcifications within intracerebral regions such as in the basal ganglia.
Biochemical investigations are helpful in identifying the cause of hypocalcaemia and establishing the cause (Figure 1). For example, in hypoparathyroidism, serum calcium is low, phosphate is high, and PTH is low; renal function and concentrations of the 25- hydroxy and 1,25- dihydroxy metabolites of vitamin D are normal. The features of pseudohypoparathyroidism (PHP) are similar to those of hypoparathyroidism except for PTH, which is markedly increased. In chronic renal failure, serum phosphate is high and alkaline phosphatase, creatinine and PTH are elevated; 25- hydroxyvitamin D is normal and 1,25- dihydroxyvitamin D is low. In vitamin D deficiency and osteomalacia, serum calcium, and phosphate are low, alkaline phosphatase and PTH are elevated, renal function is normal, and 25- hydroxyvitamin D is low.
Fig1. Clinical approach to the investigation of common causes of hypocalcaemia. CKD, chronic kidney disease; eGFR, estimated glomerular filtration rate; 25OHD, 25- hydroxyvitamin D. Adapted with permission from Hannan FM, Thakker RV. Investigating hypocalcaemia. BMJ. 2013;346:f2213. Copyright © 2013, British Medical Journal Publishing Group. (ref 2).
