Influence of measurement time delay on the ionized calcium concentration according to blood gas analysis ―Lactate values increase and ionized calcium values fall when the gas analysis syringe is left at room temperature for 3.5 hours―

Abstract

［Objective］ Serum ionized Ca (iCa) level measurements acquired using the ion‒selective electrode method should be obtained within 3 to 4 hours. In whole‒blood gas analysis, the influence of delaying iCa measurements for ＞3 hours was investigated. ［Method］ In 43 hemodialysis patients, 2 mL of whole blood was drawn from an internal shunt before dialysis using a balanced heparin‒coated syringe, and gas analysis was performed promptly. The sample was left for 3.5 hours at room temperature, and then gas analysis was performed again. ［Results］ Comparing the values obtained before and after the sample was left for 3.5 hours revealed the following changes： pH： from 7.375±0.034 to 7.304±0.035, HCO₃： from 20.20±1.85 to 19.91±1.80, base excess： from －4.38±1.85 to －6.10±1.89, pCO₂： from 35.39±3.72 to 40.81±4.12, and lactate from 1.32±0.34 to 3.02±0.44 (all p＜0.001). Despite the presence of acidosis, the subjects’ iCa and pH‒corrected iCa levels decreased from 1.13±0.07 to 1.12±0.08 (p＜0.03) and from 1.12±0.07 to 1.08±0.08 (p＜0.001), respectively. ［Conclusion］ Delaying whole‒blood gas analysis for 3.5 hours resulted in increased lactate, decreased pH, and decreased pH‒corrected iCa levels.