Cleaning indicators for dishwasher disinfectors and ultrasonic cleaners – guidance in accordance with ISO .
Why is cleaning verification critical in healthcare and sterilization technology?
Cleaning is the first and most critical step in the reprocessing of medical devices. If cleaning fails, subsequent disinfection and sterilization cannot be reliable—regardless of the method used. Therefore, systematic monitoring of cleaning processes is a fundamental requirement in healthcare, central sterilization departments, dental care, and laboratory operations.
Automated dishwashers, rinse disinfectors, and ultrasonic cleaners can be affected by variations in time, temperature, mechanical factors, water quality, and chemical dosing. Cleaning indicators are used to verify that the process actually works in practice—not just in theory.
Different instruments require different cleaning methods
Medical instruments come in many forms—such as orthopedic, gynecological, urological, dental, and neurosurgical instruments—with varying geometries, materials, and levels of complexity.
The contaminants to be removed may include:
- Blood and protein residues
- Fat and carbohydrates
- Bone fragments, cement, and mucus
These have different chemical and physical properties and therefore require different cleaning regimens, such as enzymatic, alkaline, or nonionic detergents, as well as appropriate cleaning times and temperatures.
What do the standards say? (ISO , HTM, and AAMI)
International and national standards set clear requirements for cleaning control:
- ISO and ISO – Requirements for dishwasher-disinfectors and validation of cleaning
- HTM-01-01 and HTM-01-05 – UK guidelines for decontamination
- ANSI/AAMI ST79 – American standard for sterile technical practices
ISO describes, among other things, 19 different types of test soils that can be used in the validation of cleaning processes. So-called surrogate cleaning indicators are used for routine monitoring.
What is a cleaning indicator?
A cleaning indicator is a validated testing aid that simulates hard-to-remove dirt on medical devices. It is used to monitor and document the effectiveness of the cleaning process on a daily basis.
An optimal cleaning indicator should be:
- Fast
- Sensitive
- Meticulous
- Reproducible
- Robust
- Easy to use and interpret
It must also meet the following requirements:
- Removed completely when cleaned properly
- Do not remove if any critical parameter fails (time, temperature, dosage, water quality)
- Do not generate biological or hazardous waste
Different levels of cleaning difficulty – CDWA3 and CDWA4
Terragene® offers Chemdye® Splat cleaning indicators in two levels of sensitivity:
- Chemdye® Splat CDWA3, blue– for tough cleaning challenges
- Chemdye® Splat CDWA4, pink– extremely difficult to clean
The indicators consist of a synthetic substrate printed with naturally colored substances such as proteins, carbohydrates, and fatty acids. The test dirt is non-toxic, water-soluble, and follows the flow of the washing solution.
Holders that simulate real instruments
To simulate real-world cleaning conditions, special holders are used:
The holders are designed to simulate:
- Shaded surfaces and hinges
- Indirect impact on water
- Mechanical barriers against the water jets from the sprinklers
They can be secured in the dish rack for consistent placement, which is essential for validation and comparability over time.
How to Choose the Right Cleaning Indicator – Step by Step
To determine which indicator is suitable for routine monitoring, a cleaning performance test/validation test must be performed.
Recommended method:
- Always start with the most demanding Chemdye® indicator—CDWA4, pink
- Place indicators at various levels and positions in the machine
- Run the validated cleaning program (only the cleaning phase is evaluated)
Document:
- Time and Temperature
- Type and dosage of cleaning agent
- Water quality and water pressure
- Seating in the chamber
- Visual result
The indicator is approved for routine inspection when:
- It clears completely in all positions when the cycle is correct
- It does not reset during an intentional fault cycle
What is a faulty bicycle?
A fault cycle involves the deliberate degradation of at least one critical parameter, for example:
- No detergent required
- Temperature too low
- Cleaning time cut in half
Tip: Flush the system with water before testing—residues in hoses and pumps can otherwise cause false positive results.
IfChemdye® CDWA4 (pink)does not perform correctly, adjust the process and repeat the test. If CDWA4 is too sensitive, Chemdye® CDWA3 (blue)may be the right choice.
When is revalidation of the cleaning indicator required?
A new validation must be performed when:
- Cleaning schedule changed
- Load type or instrument is changed
- The machine is being serviced or repaired
Summary – Safe cleaning starts with the right indicator
By using the correct cleaning indicator for routine checks, you ensure:
- Compliance with ISO and other international standards
- A traceable and documented cleaning process
- Improved patient safety
- Requirements for effective disinfection and sterilization
Choosing the right cleaning indicator provides assurance that the cleaning process—the most critical step in the sterile supply chain—is truly effective.
This article is based on the Terragene® guidance document: “How to Correctly Select a Cleaning Indicator,” Rev. 1 (December 2021). Download the article (PDF, 3MB)
Do you need help choosing the right cleaning indicator for your process?
Contact Hygiene Diagnostics for advice and validation support.