Laboratory Accreditation Section Identifier

Laboratory Accreditation

Using Digital Reference Thermometers
in Microbiology Testing Laboratories

Washington state will allow accredited microbiological laboratories to use digital reference thermometers, so long as they meet the Digital Reference Thermometer Requirements, as below.

Digital Reference Thermometer Requirements

Digital reference thermometers may be used in accredited microbiology laboratories under the following conditions:

  • They must be certified by the National Institutes of Standards and Technology (NIST), traceable to NIST, or conform to NIST specifications.
  • The stated accuracy must be ± 0.05 or better.
  • They must be checked by ice-point calibration with each use. If ice point temp is off, they must be sent out for recalibration/recertification before use.
  • They must be recalibrated/recertified as recommended by manufacturer or as on the calibration certificate. This must be every five years, at a minimum.
  • They must be recalibrated/recertified at the temperatures used for annual thermometer calibration checks for in-use thermometers.

Mercury-in-glass thermometers are becoming more difficult to find or to have shipped into Washington State, even though they are legal to use for laboratory calibration, and digital thermometers lose calibration much more easily through rough handling. Accredited microbiological laboratories must follow the guidelines above when using digital thermometers, and should handle all thermometers with great care.