The effect of temperature on plasma ionized calcium measured in whole blood in vitro

Abstract

Plasma calcium ion concentration (cCa²⁺) in samples from 50 healthy volunteers was measured at four temperatures (21, 26, 31 and 37°C) using a calcium electrode based on a neutral carrier ligand. A small negative correlation was found between temperature and cCa²⁺, the coefficient being −0.0017 mmol·l⁻¹·°C⁻¹ (P<0.001). The significance of this in clinical, physiological and instrumentation fields is discussed.

The effect on measured cCa²⁺ of overnight storage at 4°C was slight, but did increase the variance of the results. It is suggested that the most accurate results of cCa²⁺ will be obtained from fresh samples measured at body temperature.

Key-words:

• cardiac surgery
• hypothermia
• ion-selective electrode
• normal values
• sample storage
• temperature coefficient