Chemical Indicators (Internal and External)

Chemical indicators (Table 4) use sensitive chemicals to assess critical variables (e.g., time, temperature, or steam saturation) during a sterilization cycle. They are applied either to the outside or placed on the inside of each instrument unit (e.g., packs, peel pouches, containers, etc). They do not prove that sterilization has been achieved, but they can provide an early indication of a problem and where in the sterilization process the problem might exist.2,3

Table 4. Classification (non-hierarchical) of chemical indicators.3
Class 1: Process indicators.
  • Process indicators are applied to the outside of a unit.
  • It is designed to react to one critical variable, usually temperature.
  • A color change indicates that the unit has been directly exposed to the sterilization process and helps to distinguish between processed and unprocessed units.

    Examples: ProChek® ID Indicator Tape
    ProChek® ID Dry Heat Sticker
Class 2: Indicators for use in specific tests (e.g., air removal).
  • An air-removal indicator is positioned over the chamber drain of an otherwise empty sterilizer.
  • It is designed to assess air removal from the chamber of a high-speed prevacuum sterilizer.
  • An uneven color change indicates an inefficient air removal stage, an air leak, or non-condensable gases in the steam supply.

    Example: AirView Bowie-Dick Test Pack
Class 3: Single-parameter indicators.
  • Single-parameter indicators are placed on the inside of a unit.
  • It is designed to react to one of the critical variables, either time or temperature.
  • A color change indicates that the unit has been directly exposed to the chosen variable during the sterilization process.

    Example: ProChek® ID Paper Strip
Class 4: Multi-parameter indicators.
  • A multi-parameter indicator is placed on the inside of a unit.
  • It is designed to react to two or more of the critical variables, usually time and temperature or time, temperature or steam.
  • A color change indicates that the unit has been directly exposed to the chosen variables during the sterilization process.

    Examples: Sure-Check® Strips
    Sure-Check® Sterilization Pouches
Class 5: Integrating indicators.
  • An integrating integrator is placed on the inside of a unit.
  • It is designed to react to all critical variables and to correlate to biological indicators (BIs).
  • A color change indicates that the unit has been directly exposed to the chosen variables during the sterilization process.

    Examples: STEAMPlus Class 5 Integrator
    ProChek® S Class 5 Indicator
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