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.