Background: Serum total carbon dioxide (TCO₂) measurements are easily affected by numerous factors. Whether an irregularly high atmospheric CO₂ concentration affects the TCO₂ measurement remains unclear.

Materials and Methods: In Somdech Phra Debaratana Medical Center laboratory (SDMC) and the main building laboratory (Building 1) located within Ramathibodi Hospital, Mahidol University, Bangkok, Thailand, the repeated TCO₂ measurements using an enzymatic assay in three levels of human based control material were performed every two hours, over a one-day period. TCO₂ in a total of 150 patient sera were measured. Simultaneously, atmospheric CO₂ levels were determined.

Results: Atmospheric CO₂ levels in SDMC and Building 1, ranged from 763 to 1,560 ppm and 602 to 787 ppm, respectively. Repeated TCO₂ measurements for SDMC, the measured TCO₂ concentrations of all control materials clearly increased between 10:00 a.m. and 4:00 p.m., with the peak at 2:00 p.m., which was related to an increase in the atmospheric CO₂ concentration. By contrast, in Building 1, the measurements were considerably stable. Moreover, considering patient data (n=12,042), the estimate median TCO₂ concentration in SDMC was likely to increase between 10:00 a.m. to 4:00 p.m. as well. The association between the bias (y), difference TCO₂ concentration obtained between the SDMC and the Building 1, and the increasing atmospheric CO₂ (x) was y = 0.0038x – 0.016, R²=0.6813. Using regression equations, TCO₂ level increased by approximately 0.4 mmol/L for every 100 ppm of CO₂ increase in atmosphere.

Conclusion: High atmospheric CO₂ concentrations can result in falsely high TCO₂ values, which may lead to markedly wrong interpretations, especially in patients with a tendency to have low TCO₂ concentrations.

Keywords: Serum total carbon dioxide, Atmospheric carbon dioxide, Acid-base disorder

DOI: doi.org/10.35755/jmedassocthai.2020.08.11183

Received 6 Mar 2020 | Revised 25 May 2020 | Accepted 27 May 2020