Calcium Disturbances

You need to determine the following when a patient presents with a suspected calcium disturbance:

Total plasma calcium

The reference range is 2.2-2.6mmol/l.

Plasma phosphate
  • The reference range is 0.8-1.4mmol/l
  • It is essential to biological systems
  • Plasma phosphate levels are low in primary hyperparathyroidism
  • High levels of plasma phosphate are found in renal failure and hypoparathyroidism
Urinary calcium
  • The normal range is 2.5-7.5mmol/24h
  • Urinary calcium is clearly increased in hypercalcaemia and where renal absorption is decreased
  • In familial hypocalciuric hypercalcaemia, urinary Ca2+ is inappropriately low with high serum calcium levels
  • In clinical practice, urinary calcium collection is useful in the investigation of renal colic patients
Parathyroid hormone measurement

Raised levels of PTH are found in:

  • Primary, secondary and tertiary hyperparathyroidism
  • Familial hypocalciuric hypercalcaemia
  • Lithium toxicity
25-hydroxyvitamin D
  • Serum 25-OHD levels allow determination of vitamin D status in the body
  • Vitamin D insufficiency or deficiency is usually associated with an increase in serum PTH
Alkaline phosphatase

Serum levels increase when calcium is mobilised from bone in osteomalacia, Paget’s disease and secondary hyperparathyroidism.