Outdoor Courier Lockboxes in Summer Are a Significant Source of Preanalytical Error

Megan E. Dibbern, MD; Christina C. Pierre, PhD; Joesph R. Wiencek, PhD


Am J Clin Pathol. 2021;156(5):866-870. 

In This Article


The real-time temperatures in both cold and warm lockbox conditions were compared with ambient temperature for both studies. The mean cold and warm lockbox temperature conditions for the uncentrifuged study were 22.3°C (range, 16.5–22.3°C) and 42.6°C (range, 34.4–46.9°C), respectively, with a mean ambient outdoor temperature of 40.4°C (range, 28.2–44.0°C). The mean cold and warm lockbox temperatures for the centrifuged study were 18.0°C (range, 12.2–23.0°C) and 35.2°C (range, 25.9–40.8°C), respectively, with a mean ambient outdoor temperature of 37.9°C (range, 27.2–46.3°C).

Several analytes were noted to be outside SCLs in all conditions studied (Supplemental Tables 1 and 2; all supplemental material can be found at American Journal of Clinical Pathology online). In both studies, the most common analytes to cross SCLs were aspartate aminotransferase, glucose, LDH, and potassium Figure 1. Uncentrifuged samples that were left to sit in the outdoor courier lockboxes before being centrifuged and analyzed showed a greater difference between the cold and warm conditions than the centrifuged samples (Supplemental Table 3). The most pronounced difference was noted at 4 hours. The mean concentrations and mean standard deviations for each study and each examined analyte are summarized in Supplemental Tables 1 and 2.

Figure 1.

Mean percent difference in the concentration of 4 analytes over time in each condition. The 4 analytes that exceeded the significant change limit at some or all timepoints were aspartate aminotransferase (AST), glucose, lactate dehydrogenase (LDH), and potassium; the mean percent difference in their concentrations was compared over time. The mean percent difference for AST, glucose, and LDH concentrations increased from 1 hour to 4 hours in cold storage uncentrifuged (A) and cold storage centrifuged (B) as well as in warm storage uncentrifuged (C) and warm storage centrifuged (D).

Publicly available instructions for lockboxes were inconsistent between institutions reviewed (Table 1). None of the clinical laboratories included time restrictions for samples placed in lockboxes, and 2 had clear statements only about inappropriate outdoor temperatures for lockbox use. Other notable variations in instructions were lockbox placement and number of cold packs.