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Hot temperatures in outdoor lockboxes increase sample errors


 

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, said in an interview.

Dr. 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, Dr. 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, Dr. 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,” Dr. Wiencek said.

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