Exp Mol Med.  2003 Feb;35(1):17-22.

Enzymatic method for assaying calcium in serum with Ca++-ATPase

• Javed HM
• Michelangeli F

Abstract

A kinetic assay for total calcium in serum was developed which is based on the activation of Ca++-ATPase by free Ca++ [Ca++]f maintained by EGTA in the reaction mixture. The concentration of Caf++ was dependent on total reference calcium added or serum calcium. Ca++-ATPase activity was coupled to the reduction of NADH by pyruvate kinase (PK) and lactate dehydrogenase (LDH) and monitored by change in absorbance at 340 nm. The calcium in normal serum was 10.08 +/- 0.24 mg/ dl (n = 35) by our method while with o-cresolphthalein complexone (CPC) method, the total calcium in the same 35 serum samples was 10.14 +/- 0.54 mg/dl. The range of within-run coefficient of variations (CVs) by this method was 0.9-2.87% at 8-12 mg/dl and day-to-day CVs were 0.72-3.17%. The presence of other ions and standard clinical interfering agents did not affect this assay system. The correlation between values obtained with our method (y) and CPC method (x) for normal serum was: y = 1.064x-0.580 mg/dl (r = 0.912, n = 59).

Keyword

Ca++ -ATPase; calcium; serum; enzymatic assay; kinetics

MeSH Terms

Adenosinetriphosphatase/metabolism
Adolescent
Adult
Calcium/*blood
Comparative Study
Enzyme Activation
Female
Human
Kinetics
Male
NAD/metabolism
Pyruvate Kinase/metabolism
Reference Standards
Reproducibility of Results
Sensitivity and Specificity