Quality control of total carbon dioxide (CO₂) in serum or plasma using the Abbott Architect is affected by...

Introduction: Total CO₂, 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 CO₂ during periods of high personnel attendance. A qualitative analysis revealed a correlation between atmospheric CO₂ in the lab environment and the acquired total CO₂ value in a quality control sample. Assessment of total CO₂ is hence influenced by the equilibrium between atmospheric CO₂, dissolved CO₂ and bicarbonate. The effect is more pronounced on samples containing low concentrations of total CO₂. The bias related to environmental CO₂ is also noticeable on patient samples, patient means between periods with high and low atmospheric CO₂ 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 CO₂ 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.