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

Abstract and Introduction


Objectives: To determine the impact of short-term (<4-hour) exposure of summer-like temperatures on lithium heparin (uncentrifuged and centrifuged) samples stored in outdoor courier lockboxes in the Mid-Atlantic United States.

Methods: Healthy adults (n = 8) were recruited to investigate the impact of the short-term exposure of lithium heparin samples (centrifuged and uncentrifuged) inside 2 LabLocker-KF300 courier lockboxes placed outside in direct sunlight during summer. Each courier lockbox was monitored every 5 minutes with a temperature data logger and contained either the standard number (n = 2) of cold packs (cold) or no standard cold packs (warm). Acceptable tolerance limits were defined for each analyte by significant change limit (SCL) analysis (P < .05), as previously described.

Results: Significant changes were identified in each study condition for warm and cold lockbox conditions. Aspartate aminotransferase, glucose, lactate dehydrogenase, and potassium commonly crossed SCLs from mean baseline (t0) in the majority of conditions.

Conclusions: Outdoor courier lockboxes are an underrecognized source of preanalytical error.


Declining reimbursement for health care has resulted in many institutions consolidating testing to a central, core laboratory.[1,2] This approach provides advantages, such as the ability of larger systems to withstand economic downturns, cost savings through volume discounts, standardization in methodologies and reporting, and comparability of all laboratory test results across health care sites.[2,3] One challenge to laboratory consolidation, however, is external sample transport, with catchment areas for institutions reaching up to hundreds of miles.[4] A common approach for many health care systems is to employ courier services to retrieve patient samples from satellite clinics, with samples then stored in lockboxes for transport to the core laboratory.[5]

Initial investigations have started to characterize preanalytical variability associated with these sample transport processes. With outdoor storage, lockboxes can be exposed to variations in ambient seasonal temperature, which can vary widely depending on latitude, season, and even sunlight exposure.[5] Additionally, delays in courier pickup—because of traffic, incorrect directions, and motor vehicle crashes, for example—can also be unpredictable and systemic. These situations can result in samples sitting in outdoor lockboxes for an unexpected amount of time, which inevitably exposes those samples to wide variations in ambient temperature.[5]

To date, no available standards or guidelines exist for outdoor courier lockboxes, such as (1) sample storage time limits, (2) design and insulation, (3) outdoor placement, or (4) monitoring and maintenance of lockbox temperatures during summer or winter conditions.[5–7] Therefore, our goal was to determine the impact of short-term (<4-hour) exposure to ambient summer temperature on lithium heparin samples (uncentrifuged and centrifuged) stored in outdoor lockboxes.