Quality control of total carbon dioxide (CO 2 ) in serum or plasma using the Abbott Architect is affected by environmental pCO 2 concentrations

Introduction: Total CO 2 , or bicarbonate, is a parameter in clinical chemistry often applied to assess the metabolic status of a patient. This article discusses the observations and interventions during an episode of assay instability on an Abbott Architect routine chemistry analyser. Results: The Levey–Jennings plot of QC data showed a circadian pattern, having an overestimation of total CO 2 during periods of high personnel attendance. A qualitative analysis revealed a correlation between atmospheric CO 2 in the lab environment and the acquired total CO 2 value in a quality control sample. Assessment of total CO 2 is hence influenced by the equilibrium between atmospheric CO 2 , dissolved CO 2 and bicarbonate. The effect is more pronounced on samples containing low concentrations of total CO 2 . The bias related to environmental CO 2 is also noticeable on patient samples, patient means between periods with high and low atmospheric CO 2 levels differed by 2 mmol/L. Discussion: Passive ventilation of the laboratory environment is proven insufficient during weather conditions in which the lab is not exposed to wind. Consistent reduction of atmospheric CO 2 could only be guaranteed with an active ventilation infrastructure. Systematic closure of analyser lids also reduced analyser variance. Conclusion: The lab environment is an important source of parameter variance. Both environmental and infrastructural aspects must be considered when assessing the potential cause of the instability.