Diagnostic Use
Increased calcium concentrations: primary and tertiary hyperparathyroidism, malignancies (both with and without bone involvement), sarcoidosis, vitamin D overdosage, dehydration, Paget’s disease (with immobilisation) and genetic disorders of the calcium sensing receptor.
Decreased calcium concentrations: hypoparathyroidism, pseudohypoparathyroidism, chronic renal failure, renal tubular disorders, magnesium deficiency, vitamin D deficiency, prolonged anticonvulsant therapy, acute pancreatitis, rickets and osteomalacia.
Corrected or adjusted calcium
The routine test for plasma calcium concentration measures the total calcium (bound plus ionised calcium ). Approximately 50% of plasma calcium is bound to albumin, and this bound fraction is biologically inactive. Therefore changes in albumin concentration will affect the total calcium concentration without affecting the ionised (active) fraction of plasma calcium.
In order to allow the use of a single reference interval for total calcium, irrespective of albumin concentration, the total calcium can be adjusted using a formula. This is known as the “corrected” or “adjusted” calcium.
The formula used at MMH laboratory is (ref 1)
[Ca adjusted] = [Ca total] + 0.012 x (39.9 – [albumin (BCP assay)])
Test Method
Principle: 5-nitro-5'-methyl-BAPTA (NM-BAPTA)
Analyser: Roche Diagnostics Cobas c703/c503
Reagent: CA2
Limitations / Interference
Prolonged stasis during venepuncture and haemolysis will give false high values.
Albumin is always be measured in conjunction with calcium.
Fasting for 12 hours and seated for 20 minutes prior to venepuncture are preferred for accurate baseline level.
Ionised calcium is the gold standard test to assess calcium status.