EVALUATION OF A NEW AUTOMATIC CALCIUM-ION ANALYZER

Abstract

A new automatic analyzer for Ca2+, the Orion Model SS-20, based on a flow-through ion-exchange electrode, was evaluated. Ca2+ was measured in heparinized human whole blood and serum. Within-day variation was 1.2%, day-to-day variation 1.6% and analytical recovery 92.4%. Over the physiological range interference by K+ and Mg2+ was negligible; major changes in ionic strength, induced by changes in Na+ concentration, made correction for a Na+ error necessary. Within the physiological range, Ca2+ was inversely correlated to variations in pH. Therefore, to compare Ca2+ values, correction to an apparent pH of 7.40 should be made. The Ca binding effect of heparin was negligible when minimal (4.4 IU/ml) concentrations of heparin were used. Storage of serum at 4.degree. C for 1 wk resulted in a 4% decrease in apparent serum Ca2+, primarily owing to an increase in pH during storage. In normal material, mean values for blood- and serum-Ca2+ (1.10 and 1.07 mmol/l, respectively) were close to results obtained by previous systems. Errors caused by disturbances in the fluid flow and non-function of half the electrodes received were the major inconveniences of the analyzer. This new analyzer gives decisive advantages in measurement of Ca2+, making this important analysis possible as a routine laboratory test for the 1st time.