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KMID : 0384119940140010012
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Korean Journal of Clinical Pathology
1994 Volume.14 No. 1 p.12 ~ p.19
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Determination of Total Calcium in Serum with Arsenazo III Method
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Abstract
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Background : Most clinical laboratories use spectrophotometric methods for determining calcium. Of several available colorimetric reagents, the o-cresolphthalein complexone (OCPC) method is used by the majority of clinical laboratories Utility of
the
OCPC assay is limited by the fact that absorption of carbon dioxide by the alkaline reagent causes considerable calibration drift. Arsenazo III is highly sensitive and specific for calcium, generating a sensitive absorbance peak at (600-660 nm.
Because
the Arsenazo III reacts under slightly acidic conditions, bicarbonate absorption is greatly decreased and so calibration stability is enhanced. We evaluated a method based on the use of Arsenazo III that would yield accurate results in normal,
icteric,
hemolyzed, and lipemic samples.
Methods : All photometric analyses were carried out with the Hitachi 747 autoanalyzer (Hitachi, Tokyo, Japan) at 37℃ with Arsenazo III, 200μmol/L in 50mmol/L 1,4-piperazinediethanesulfonic acid (PIPES) buffer.
Results : The within-run CVs at calcium concentrations of 4.1. 8.1, and 16.2 mg/dL were 2.5, 1.0, and 1.1%, respectively, and the corresponding between-run CVs were 2.8, 1.7, and 1.4%. The standard curve for calcium was linear from 4 to 16 mg/dL.
Results for 345 patients' samples, calcium range 4.9-10.8 mg/dL, showed good agreement with the results by the OCPC method. The Arsenazo III method showed no interference from as much as 35.1 mg/dL of bilirubin and 10 g of hemoglobin per liter.
Calibration was stable for 3 weeks with use of open reagent in the instrument.
Conclusions : The method with Arsenazo III has several advantages including pathophysiologically acceptable linearity, increased stability, and essentially no interference from hemolysis, lipemia, and icterus. (Korean J Clin Pathol 1994 14(1) :
12-9)
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