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

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