Spirited away: Can ethanol testing in add-on orders provide meaningful results?

Ethanol is a volatile substance, and specimens need to be tightly capped prior to analysis to prevent evaporative loss. However, add-on requests in previously decapped tubes are commonly received, yet ethanol stability in this setting is unclear. We compared the stability of ethanol in capped vs decapped tubes in the context of routine laboratory automation, storage time, and specimen volumes. Serum specimens were pooled and spiked with ethanol followed by simulating an add-on scenario. Additionally, to evaluate ethanol stability at room temperature for extended times, ethanol concentrations were measured in capped or decapped tubes containing 0.5 mL or 0.1 mL samples over a 4 h time course. Finally, the risk of misclassification of ethanol results in decapped tubes was evaluated near the critical value threshold (∼54 mmol/L). The add-on tubes had a mean recovery of 101.5 % (95 % CI: 97.7-105.4 %) relative to the direct tubes. The time-course experiment showed an average recovery of 87.4 % (95 % CI: 81.8-94.0 %) at the 4 h time point in decapped 0.5 mL specimens. An average recovery of 85.4 % (95 % CI: 84.2-86.1 %) was observed for specimens spiked near the critical value threshold. Importantly, all measurements with 0.5 mL specimen volume were within 25 %, which is the total allowable error (TAE) of the assay.However, with a 0.1 mL volume, specimens cross the TAE threshold just after 1 h, and the percent recovery at 4 h dropped to 52.9 % (95 % CI: 50.2-55.7 %). In conclusion, ethanol testing in decapped tubes remains within the TAE for up to 4 h in specimens with a 0.5 mL volume. Therefore, add-on ethanol testing using routine laboratory automation and storage conditions can be successfully performed.