Chemical indicators for sterilization-what are they and their types?

Indicator

An indicator is an observable characteristic that can be used to show changes toward achieving a specific outcome.

Chemical indicator

Chemical indicator undergoes an observable change when conditions change. This could be a color change, temperature change, or other measurable quality.

Benefits of using chemical indicators for Sterilization

These chemical indicators are used in sterilizers in Pharmaceuticals / laboratories / hospitals / medical devices manufacturer. At the end of the sterilization cycle, the colour change in the indicator would indicate that the sterilization cycle is satisfactory or not?

Indicator strips / chemical indicators play a critical role in sterility assurance program by assuring that the sterilizer is working as per the set sterilization conditions.

They are used to monitor whether the parameters to achieve sterilization have been met for a specific sterilization process.

Note that, chemical indicators alone do not confirm that an item is sterile. Chemical indicators must be used as part of Quality program that should also include the use other sterilization physical monitoring and biological indicators to assure that the conditions for sterilization were met.

When chemical indicators are used as part of the established quality program, they can capture failures, such as malfunctioning equipment that could result in a non-sterile device / aid / product. 

How they work

Chemical indicators use one or more chemicals that undergo either a physical or chemical change that is visible to the human eye, after exposure to predetermined critical parameters such as time, temperature and sterilant.

Usage of the chemical indicators

Chemical indicators are used in all types of sterilization processes like steam, hydrogen peroxide, and ethylene oxide.

Basis of classification – ISO-11140-1:2005

The basis of classification of chemical indicators for sterilization is as per EN ISO 11140-1:2005, Sterilization of healthcare products-Chemical indicators-Part 1: General requirements.

It defines six classes of Chemical Indicators. They are classified based on the sterilization process as per the design of use.

The classification structure used is to denote the characteristics and intended use of each type of indicator when used as defined by the manufacturer. This classification has no hierarchical significance.

This means that the class number does not mean that one class is necessarily better or measures more parameters of the sterilization process than another class.

Chemical Indicator classifications enable the end user to understand performance parameters. The appropriate Chemical Indicator can then be used to obtain the information needed to determine the effectiveness of the sterilization process.

Types of chemical indicators

Class 1: Process Indicators

These are classified as process indicators and intended for use with individual units (e.g. packs, containers) to indicate that the unit has been directly exposed to the sterilization process and to distinguish between processed and unprocessed units. They shall be designed to react to one or more of the critical process variables.

Examples – Indicator tapes, indicator labels are examples of externally visible Chemical Indicators that are Process Indicators used for exposure control.

What they indicate– Exposure to the sterilization process and help to differentiate between processed and unprocessed loads.

Class 2: Indicators for use in specific tests

Class 2 indicators are used in specific test procedures as defined in relevant sterilizer / sterilization standards.

Example: Bowie-Dick type tests are specific tests used for equipment control to evaluate the sterilizer performance.

What they indicate– For use in specific tests as defined by standards.

Class 3: Single variable indicators

A single variable indicator is designed to react to one of the critical variable and is used to indicate exposure to a sterilization process at a stated value and would not provide much information.

Example: Temperature tube that contains a chemical pellet that melts at a specific temperature. This temperature tube would be used to determine that a specific temperature was reached at a specific location in the sterilizer chamber.

What they indicate– React to one critical parameter.

Class 4: Multi-variable indicators

A multi-variable indicator is designed to react to two or more of the critical variables and is intended to indicate exposure to a sterilization process at the stated value.

Example: Strips printed with a Chemical Indicator.

What they indicate– React to two or more critical parameters.

Class 5: Integrating indicators

Integrating indicators are designed to react to all critical variables.

Example Strips printed with a Chemical Indicator.

What they indicate– React to all critical parameters over a range of sterilization cycle.

Class 6: Emulating indicators

Emulating indicators are cycle verification indicators and are designed to react to all critical variables for specified sterilization cycle.

Example: Strips printed with a Chemical Indicator. Emulating Indicators are specified for specific sterilization so that the end user will have to use a different Class 6 Indicator for each sterilization cycle time and temperature [e.g. 3 min and 15 min] run in the facility.

What they indicate– React to all critical parameters for specified sterilization cycle

Note-The images given for representation in this blog are taken from Google Images. Many thanks for Google.