Courier lock-boxes are containers primarily used for specimens awaiting transport to an offsite testing laboratory. They come in various shapes, sizes and are commonly made of thin, high-impact polystyrene or 24 gauge cold-rolled steel. The lock-boxes can be insulated with foam and/or Styrofoam in an attempt to maintain the integrity of the specimens kept inside. Most of these lock-boxes are located outside of the clinic, exposed to environmental conditions, because couriers do not have keys to the physician offices for pick-ups after hours. Delayed storage and ambient seasonal temperature conditions in lock-boxes are frequently overlooked as factors for preanalytical variation in laboratory testing and to date, no guidelines or standards exist to improve this area of the total testing process.

In our recent study, presented at the 69th AACC annual meeting, we began to characterize the effects of sample exposure to ambient temperature changes while stored in courier lock-boxes on several commonly ordered analytes during four seasons in Nashville, Tennessee (1). Impact of delayed storage, over a weekend, under these conditions was also examined, because specimens collected late on a Friday were occasionally forgotten by our courier service, which led to inquiries on Monday morning about the viability of specimens left in the lock-boxes.

To establish the seasonal temperature effects of specimens stored in courier lock-boxes, we collected paired, deidentified lithium heparin BD PST Vacutainer® tubes from healthy volunteers (n=4) during four seasons (winter, spring, summer, fall) following specific recommendations. Specimens were processed immediately after collection. Once processed, paired specimens were analyzed either in the core laboratory (t0) or after 72 hours (t72) of holding at ambient temperature in an outside courier lock-box. Temperature was continuously monitored every 15 minutes with an INKBIRD® THC-4 Temperature Data Logger. Following 72 hours, the temperature data was plotted for review. Each sample was analyzed for a Comprehensive Metabolic Panel, Lipid profile, Thyroid panel and Total Vitamin D. The percent change from baseline was determined by calculating the mean difference between each analyte concentration after storage (t72) and the mean concentration of each analyte at time zero (t0) divided by the mean time zero result multiplied by 100. The clinical impact due to seasonal ambient temperature exposure was determined by significant change limit (SCL) analysis. For each analyte tested, SCLs were calculated utilizing 12 months of cumulative performance data (coefficient of variation) multiplied by ±2.8 standard deviations as previously described (2).

The total number of temperature points recorded during each seasonal experiment in the courier lock-boxes was 265±5. The average temperatures were winter: -3.1°C (Range: -9.9-22.3°C), spring: 16.1°C (Range: 7.0-25.2°C), summer: 25.0°C (Range: 21.4-29.8°C) and fall: 10.6°C (Range 2.2-22.8°C). Deviations outside the SCL were observed for several analytes most notably glucose, K+, and AST when compared to initial measurements for all seasons. Cooler and subzero temperatures seen in fall and winter experiments showed 7/21 and 6/21 of analytes measured were outside of SCL, respectively (p<0.05 from t0). More analytes exceeded SCL in warmer seasons, 10/21 in spring and 9/21 in summer.

Currently, healthcare organizations have increasing pressure to cut costs, expand outreach services and consolidate laboratory testing to more automated core/reference laboratories (3). As a consequence, there will be a rise in the number specimens being transported from peripheral collection sites, which may result in an increase in preanalytical errors within the total testing process. This study should serve as a clarion call that specimen exposure to delayed transport and fluctuating temperatures, as experience in outside courier lock-boxes, can be sources of preanalytical variation and future studies are warranted.


  • 1.)Wiencek J and Nichols JH. Effect of seasonal temperature on specimens stored outside in courier lock boxes. Clin Chem 2017;(S10):252.
  • 2.)Boyanton BL, Blick KE. Stability studies of twenty-four analytes in human plasma and serum. Clinical Chemistry 2002;48:2242-7.
  • 3.)CAP Today. All for one, one for all? Laboratory consolidation. June 2016. (Accessed September 11, 2017)