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

Statistical Analysis

Temperature and paired, deidentified participant data were collected and analyzed in Microsoft Excel version 2008 or GraphPad Prism version software for the 2 studies. The mean for every participant and analyte was determined over the various processing, storage, and temperature conditions described. Acceptable tolerance limits for analytes were determined by significant change limit (SCL) analysis, as previously described.[5,7,8] SCLs were calculated based on the formula SCL = initial value ± 2.8 USD, where the initial value is the mean value across each participant's sample (n = 4) at t0 for each analyte and USD is the usual standard deviation of each analyte assay that was determined from 90 days of quality control (QC) performance data. The mean concentration of QC material for each analyte that was closest in concentration to the mean of the initial value (t0) was then used to select the standard deviation used in the calculation. A change in analyte concentration was considered significant (P < .05) if it exceeded SCLs.