Different Types of Chemical Indicators for Sterilization : Pharmaceutical Guidelines

Different Types of Chemical Indicators for Sterilization

Chemical indicators are used for verification of sterilization in daily routine but there are different types of chemical indicators for different types of sterilizations.
Chemical indicators have been around for a long time. Hydrangeas bloom blue used in acidic soil and bloom pink for use in basic soil, for example, are perfect indicators for soil conditions. Until 1940 to early 1950s, biological and chemical indicators were never used routinely to monitor sterilization processes. This is because earlier than 1940s; scientists believed that there was no single quality assurance method that would assure that an item is actually sterile and that it only assured that the conditions meant for sterilization have been met. However, this scientific statement is still taken as true today in many sterilization practices.

Generally, chemical indicators are either chemical or physical apparatus used to monitor a single or multiple of the process parameters of the sterilization process. They are divided into six classes.
Chemical Indicators for Sterilization
Class 1: Indicators are meant for use with individual items, for example, containers or cans to indicate that a unit has been directly subjected to the sterilization cycle and differentiate between processed and non-processed units. Indicator labels, tapes and load cards are examples external and tangible chemical indicators and are physically outside the packages.
Class 2: Under this class, the indicators meant for use in individual test procedures as indicated in relevant sterilization standards. The most popular specific testing are the Bowie-Dicks. These tests are intended to show efficacy of steam penetration and air removal.
Class 3: A specific variable indicator is created to purposely show the exposure to a single sterilization procedure at a stated value of the identified variable. For example, a specific variable is a temperature tube that hosts a chemical tablet which melts at an identified temperature.
Class 4: This class hosts multiple variable indicators. These are created to react with various critical variables and are meant to show exposure to a sterilization process at stated values of the specific variable. Examples of these indicators would be the paper strips that are used with color change chemical indicators. They are used inside every package.
Class 5: These are integrated indicators that are designed to react with all essential variables. They can be used for pack control monitoring as internal chemical indicators in all containers and packages. These can also be used as an extra monitoring tool to enable release of loads that do not have implants according to Process Challenge Device.
Class 6: These are also referred to as emulating indicators which are indicators that verify the sterilization cycle and are designed to react to all critical variables for a given cycle. They indicate the complete cycle by showing the absence or presence of certain temperature and time measurement parameters during a process. These indicators are used for steam sterilization and are only available in USA.


Chemical indicators are affordable, convenient and are used to indicate if a unit or item has been exposed to a sterilization cycle. Some case studies have shown that chemical indicators are more reliable and likely than biological indicators to show in an accurate manner, the sterilization process at marginal times, like two minutes.

In 2005, AAMI began to apply the new ISO11140-1:2005 Sterilization of healthcare items – Chemical Indicators – Part 1. This specific standard was later approved by ANSI as standards for all US states because it represented a general consensus. The major changes are performance requirements for class 1, process indicators for vaporized hydrogen peroxide process of sterilization, upgrades performance requirements for class 5 and addition of class 6 indicators.





Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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