Hot Mail: Temperature Exposure during Mail Return of an Immunochemical Fecal Occult Blood Test.

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Fecal immunochemical tests (FITs) are widely used for colorectal cancer (CRC) screening; however, high ambient temperatures were found to reduce test accuracy. More recently, proprietary globin stabilizers were added to FIT sample buffers to prevent temperature-associated hemoglobin (Hb) degradation, but their effectiveness remains uncertain. We aimed to determine the impact of high temperature (>30°C) on OC-Sensor FIT Hb concentration with current FITs, characterize FIT temperatures during mail transit, and determine impact of ambient temperature on FIT Hb concentration using data from a CRC screening program.

FITs were analyzed for Hb concentration after in vitro incubation at different temperatures. Data loggers packaged alongside FITs measured temperatures during mail transit. Separately, screening program participants completed and mailed FITs to the laboratory for Hb analysis. Regression analyses compared the impact of environmental variables on FIT temperatures and separately on FIT sample Hb concentration.

In vitro incubation at 30 to 35°C reduced FIT Hb concentration after >4 days. During mail transit, maximum FIT temperature averaged 6.4°C above maximum ambient temperature, but exposure to temperature above 30°C was for less than 24 hours. Screening program data showed no association between FIT Hb concentration and maximum ambient temperatures.

Although FIT samples are exposed to elevated temperatures during mail transit, this is brief and does not significantly reduce FIT Hb concentration. These data support continuation of CRC screening during warm weather with modern FITs with a stabilizing agent when mail delivery is ≤4 days.
Original languageEnglish
Pages (from-to)615–626
Number of pages12
JournalClinical Chemistry
Issue number6
Early online date26 May 2023
Publication statusPublished - Jun 2023


  • Fecal immunochemical tests (FITs)
  • colorectal cancer (CRC) screening
  • high ambient temperatures
  • hemoglobin degradation


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