What Is the Difference Between Chemical and Biological Indicators?
Completing a sterilization cycle is not the same as verifying that the sterilization process was carried out correctly.
Two important components of the sterility assurance system in central sterile services departments are chemical indicators and biological indicators.
Both product groups are used to monitor the sterilization process, but they do not provide the same information.
So rather than asking “chemical indicator or biological indicator?”, it is important to understand the role each of these control methods plays in the sterility assurance system.
What Is a Chemical Indicator?
Chemical indicators are control products that show a physical or chemical change when exposed to specific process variables during sterilization.
The most easily observed change is usually a change of colour.
ISO 11140-1 defines general performance requirements and test methods for indicators that show, through a physical and/or chemical change, whether one or more parameters of the sterilization process have been reached.
But there is an important distinction here:
A chemical indicator reaching the correct result does not on its own prove that the product is sterile.
A chemical indicator provides information about the targeted process conditions.
The CDC also notes that mechanical and chemical indicators do not guarantee sterilization on their own, but play an important role in detecting process failures and equipment problems.
What Is a Biological Indicator?
Biological indicators are test systems containing microorganisms or spores with known resistance to the sterilization process.
The aim is to evaluate the microbial inactivation capacity of the sterilization cycle.
ISO 11138-1 sets out the general requirements for the manufacture, labelling, test methods and performance characteristics of biological indicators used in the validation and routine monitoring of sterilization processes.
When choosing a biological indicator, a system suitable for the sterilization method in use must be selected.
For example, steam, ethylene oxide and hydrogen peroxide-based sterilization processes do not share the same operating conditions.
The biological indicator must therefore be compatible with the sterilization process it will be used in.
The Key Difference Between Chemical and Biological Indicators
Put simply:
A chemical indicator evaluates exposure to process conditions.
A biological indicator provides a control aimed at directly assessing, microbiologically, the capacity of the sterilization process to inactivate microorganisms.
These two approaches are not alternatives to each other.
They form different layers of the sterility assurance system.
Physical Monitoring Is Also Part of the Process
It is also not correct to limit sterilization control to chemical and biological indicators alone.
The sterilizer’s physical data, such as:
- cycle time,
- temperature,
- pressure,
- process phases,
- error logs,
- cycle printouts generated by the device
should also be evaluated.
The CDC treats monitoring of sterilization processes with mechanical/physical, chemical and biological indicators as parts of the sterilization control approach.
In this way, rather than drawing conclusions from a single indicator, complementary layers of control are created.
How Do You Choose the Right Indicator?
When choosing an indicator, the sterilization method in use must be determined first.
An indicator designed for steam sterilization cannot be used for the same purpose as an indicator designed for hydrogen peroxide sterilization.
The product’s
compatibility with the sterilization method, standard, indicator type, intended use and manufacturer’s instructions
must be considered together.
The Sterilizasyon Medikal product portfolio includes plasma chemical indicators as well as various biological indicators for steam, ethylene oxide and hydrogen peroxide plasma processes.
Conclusion
A sterility assurance system cannot be built on a single test or a single device printout.
A reliable process is created by properly managing the components of
physical monitoring + chemical indicators + biological control + records and traceability
.
Understanding the roles of chemical and biological indicators correctly helps evaluate possible nonconformities in the sterilization process more systematically and keep sterilization processes under control.