Hot Temperatures in Outdoor Lockboxes Increase Sample Errors

Jeff Craven

October 26, 2021

Patient samples in outdoor courier lockboxes exposed to hot temperatures for as little as 4 hours are at risk of preanalytical error, according to results from a recent study published in the American Journal of Clinical Pathology.

"Our findings indicate that samples (centrifuged or not centrifuged) were impacted by extreme summer temperatures when stored for short periods of time inside commonly used steel lockboxes," Joseph R. Wiencek, PhD, medical director of clinical chemistry, Vanderbilt University School of Medicine Core Laboratory in Nashville, told Medscape Medical News in an interview.

Wiencek and colleagues picked two dates during the summer of 2019 in a mid-Atlantic state to place two courier lockboxes (LabLocker-KF300) outside in hot temperatures (32º C) starting at 11 a.m., with one lockbox containing two 24-oz cold packs (Nordic NI24) and the other containing no cold packs. The researchers monitored the temperatures of each lockbox over the course of 4 hours.

Overall, eight participants had seven samples in lithium heparin drawn for two studies evaluating centrifuged or not centrifuged samples. In the first study, four participants had seven samples drawn, with one centrifuged sample serving as a control for each patient. The other six samples were wrapped in paper towels, placed in resealable plastic bags, and distributed evenly in the warm and cold lockboxes. The samples did not directly touch the cold packs in the cold lockbox. At 1 hour, 2 hours, and 4 hours, a participant's sample was removed from each lockbox and centrifuged.

In the second study, another four participants had seven samples drawn. As in the first study, all samples were centrifuged and placed in the lockboxes. For both studies, when samples were centrifuged, plasma from samples was left on the gel barrier when analyzed for concentrations of C-reactive protein, a comprehensive metabolic panel, lactate dehydrogenase (LDH), a lipid panel, magnesium, and phosphorus (Abbott Architect c16000).

In the study of uncentrifuged samples, Wiencek and colleagues found that when the temperature outside ranged from 28.2º to 44.0º C (mean 40.4º C), the temperature of the cold lockbox was between 16.5º to 22.3º C (mean 22.3º C). The temperature ranged between 34.4º to 46.9º C (mean 42.6º C) in the warm lockbox. For centrifuged samples, the cold lockbox temperature was between 12.2º to 23.0º C (mean 18.0º C) and the warm lockbox was between 25. to 40.8º C (mean 35.2º C) when the outdoor temperature ranged from 27.2º to 46.3º C (mean 37.9º C).

The researchers also calculated the significant change limit (SCL) for each analyte in each sample, finding that aspartate aminotransferase, glucose, LDH, and potassium significantly exceeded the SCL in both the centrifuged and uncentrifuged samples, with the greatest changes seen at the 4-hour timepoint for samples in the warm lockbox (P < .05 for all).

Lockbox Instructions Are "Consistently Inconsistent"

In viewing instructions for lockboxes across institutions, Wiencek said the "outdoor courier lockbox instructions among private, academic and reference laboratories were consistently inconsistent." For example, no laboratories cited time restrictions for samples in lockboxes, and their descriptions on the number of cold packs a laboratory should use and where the lockbox should be placed varied. The inconsistencies "highlighted the emergent need for standardization and guidance documents for institutions to implement," Wiencek said.

One unanswered question is how widespread the problem is. It is unclear how many outdoor courier lockboxes are currently in use in the United States or globally; however, experts agreed it was a common occurrence, with some of the largest laboratory service providers offering outdoor courier lockboxes to their clients.

"Courier lockboxes are everywhere. All you need to do is walk around your clinics that are at your hospitals or clinics located around your grocery store to find them," Wiencek said. "Some hang on doors, while others can be found on the ground in direct sunlight on a hot summer day."

What's more, institutions may not realize how leaving samples outdoors for extended periods can affect results. "Care teams are commonly unaware that samples placed in these poorly designed lockboxes can experience extreme summer or winter temperatures that may lead to incorrect results," Wiencek said. "Healthcare providers need to understand the hidden dangers courier lockboxes have on the quality of their patient's test results."

Amy L. Pyle-Eilola, PhD, clinical chemistry director at Nationwide Children's Hospital in Columbus, Ohio, said a major strength of the study by Wiencek and colleagues "is just that it was done at all."

"I appreciate the real-world nature of this study and that it provides a snapshot of what conditions are really like in a lockbox in the summer," she said in an interview with Medscape.

In the clinical lab, receiving samples that had been sitting a courier lockbox "is not uncommon," Pyle-Eilola said.

"When I have encountered these situations, I have struggled to decide if it is still appropriate to run the tests. I always look to the medical literature for assistance with these situations, but there has been a paucity of information available on the impact of lockbox storage," she explained.

The study by Wiencek and colleagues "provides some much-needed evidence for what is acceptable for lockbox storage conditions," she said.

Areas of Future Research

Rodney E. Rohde, PhD, university distinguished chair and professor of the Clinical Laboratory Science (CLS) Program at Texas State University in San Marcos, said in an interview that the study "does a nice job of looking at multiple analytes and controlling for several variables," but the sample size is small and the results may be difficult to generalize.

Pyle-Eilola highlighted another limitation — "a common shortcoming of these kinds of studies" — in the use of healthy donors for patient samples, which narrows the range of assay results.

"It is possible that more significant variation in results may be observed in additional analytes if the samples had higher concentrations of those analytes," she said. "Moreover, this is clinically relevant as the samples stored in such lockboxes are not always from healthy individuals and have abnormal concentrations of analytes."

Mario Plebani, MD, professor of clinical biochemistry and clinical molecular biology and chief of the department of laboratory medicine at University Hospital of Padova in Padova, Italy, agreed with that assessment.

"[T]he risks for errors and patient safety are higher for values near to the upper or lower reference value, and in general for samples collected in patients with particular diseases and clinical conditions," he said in an interview.

"This paper deserves a commenting editorial to better highlight the urgent need for further studies on the same issue and in general on the risk in the pre-pre-analytical phase, including sample storage and transportation," he noted.

Another area of future research is studying patient samples exposed to hotter or colder temperatures in outdoor courier lockboxes outside the mid-Atlantic area. "Here in Texas, temperatures can reach extreme heat levels," Rohde said, who added that use of outdoor lockboxes is "very common in my region."

Wiencek disclosed he has been a consultant on this research topic for Roche Diagnostics and received an honorarium for speaking on the subject from the American Association for Clinical Chemistry and American Society of Clinical Pathology. The other authors have no relevant conflict of interest. Pyle-Eilola, Rohde, and Plebani have disclosed no relevant financial relationships.

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

Jeff Craven is an independent journalist living in Wilmington, Delaware.

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