A reliable potentiometric measurement of ionized calcium and pH on ICA2 Radiometer in clinical practice

Abstract

A second generation analyser for potentiometric measurement of ionized calcium and pH (ICA2 Radiometer, Copenhagen) was tested with respect to analytical performance in two different laboratories. Newly-developed aqueous buffered solutions were used at different Ca²⁺ concentrations as well as biological specimens prepared from human subjects. The overall precision of ICA2 was very good: CV=0.0-0.4% for within-run and 0.4-1.7% for day-today precision with protein-free solutions and CV=0.3-0.9% for within-run precision on biological specimens. The adjusted value of Ca²⁺ to pH 7.40 is an analytical advantage for which the calculation is correct but the assumption made for this algorithm may limit its clinical relevance. Measurements were comparable on ICA2 when performed on either whole blood, serum or plasma. Pre-analytical conditions should be observed such as the choice of anticoagulant and anaerobic conditions. Such a reliable and accurate instrument may promote the use of ionized calcium measurement in daily clinical practice.

Key Words:

• analytical performance
• ion selective electrodes
• ionized calcium
• pH correction
• reference solutions