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How to Select and Place Process Challenge Devices for Steam Sterilization

Process challenge devices (PCDs) are test devices or assemblies intended to create a defined challenge to a sterilization process. Their usefulness depends on matching the device to the sterilizer, cycle, load, and monitoring question. A PCD result is one part of process assurance; it does not replace mechanical monitoring, chemical indicators, biological indicators when required, correct cleaning and packaging, appropriate loading, or complete records.[1][2]

First, identify the type of test

“PCD” is a broad term. Different devices may be intended for different applications, and they should not be treated as interchangeable merely because they contain a chemical indicator or are used in the same sterile processing department.

Air-removal and steam-penetration tests

CDC’s discussion of challenge test packs primarily addresses testing of air removal and steam penetration in dynamic-air-removal, including prevacuum, steam sterilizers. These tests are intended to present a significant challenge and are positioned in the area considered least favorable to sterilization. CDC describes challenge test packs as tools used for installation, qualification, and ongoing quality-assurance testing in the applicable context.[1]

A Bowie-Dick-type test is commonly associated with evaluating air removal and steam penetration in a dynamic-air-removal sterilizer. The specific test device, sterilizer type, cycle, placement, and interpretation must follow the device and equipment instructions and the facility’s approved procedure. A Bowie-Dick-type test should not automatically be interpreted as a test of every product or load configuration.

Type 2 indicators and small steam sterilizers

ANSI/AAMI/ISO 11140-6:2024 addresses Type 2 indicators and PCDs for performance testing of small steam sterilizers.[3] That category is distinct from a PCD selected to challenge a wrapped healthcare-product load in a larger sterilizer. The presence of a Type 2 indicator does not, by itself, establish that the device is suitable for another sterilizer, cycle, or load.

Product- or load-specific PCDs

Some PCDs are designed to represent a particular product, package, tray, container, or load challenge. Their relevance depends on the device’s stated intended use and the configuration being evaluated. A PCD intended for one challenge should not be assumed to represent all wrapped instruments, lumened devices, containers, or routine loads.

Before using any PCD, determine what the device is designed to challenge, what result it is intended to provide, and which sterilizer and cycle conditions are permitted by its instructions for use. Do not infer suitability from appearance, indicator color, or general use in the same department.

Define the monitoring question

The monitoring question should determine the selection process. Examples include:

  • Air-removal or steam-penetration testing: Is the selected test appropriate for the applicable dynamic-air-removal sterilizer and test procedure?
  • Small-sterilizer performance testing: Is the device the type specified for the relevant small steam sterilizer performance test?
  • Load or product evaluation: Does the PCD represent the particular package, tray, container, product, or configuration being evaluated?
  • Change evaluation: Does a change in packaging, load configuration, or product arrangement require a revised monitoring or qualification approach under the applicable procedure?

Routine full-load monitoring, qualification or requalification, air-removal testing, and product-specific challenge testing are related but different activities. The available CDC sources support complementary mechanical, chemical, and biological monitoring and recommend testing representative products when major changes are made; they do not establish one universal PCD approach for every sterilizer, cycle, or load.[1][2]

Match the PCD to the sterilizer and cycle

Confirm that the PCD is labeled or otherwise specified by its manufacturer for the sterilizer and cycle under evaluation. Review the instructions for use for the permitted equipment type, preparation, placement, exposure conditions, readout method, interpretation criteria, storage, usable life, and reuse status.

CDC’s cited air-removal discussion should not be generalized to mean that every PCD is validated for gravity-displacement cycles. If a facility evaluates a gravity-displacement cycle, the selected test must have an intended use and procedure applicable to that cycle. The sources provided here do not establish a universal PCD design or placement rule for gravity-displacement sterilizers.

Similarly, a PCD used in a routine load should not automatically be described as proof that every item in that load received effective sterilization. A passing indicator response shows that the indicator experienced the conditions for which it was designed. It does not independently establish sterility of all products, nor does it compensate for inadequate cleaning, unsuitable packaging, incorrect cycle selection, overloading, or failure to follow device reprocessing instructions.

Consider the load and challenge location

When the PCD is intended to evaluate a particular load or product challenge, consider the configuration that is actually being studied. Relevant features may include:

  • porous or nonporous contents;
  • instrument density and mass;
  • lumens, narrow channels, or other difficult-to-penetrate features;
  • tray, container, wrap, or pouch design;
  • load orientation and spacing; and
  • the location identified by the applicable procedure as presenting the greatest challenge.

For the dynamic-air-removal challenge testing discussed by CDC, the challenge pack is positioned in the area least favorable to sterilization and is intended to challenge air removal and steam penetration.[1][2] That guidance should be applied within its stated context. It should not be used to justify random placement or to imply that the same location is appropriate for every PCD, sterilizer, cycle, or product configuration.

Where the manufacturer or facility procedure specifies a location, orientation, surrounding load, or test condition, follow that specification. If the PCD is placed inside a tray, container, pouch, or other assembly, document the surrounding configuration so that the result can be interpreted in context.

Standardize and document use

A written procedure should identify, as applicable:

  1. the sterilizer and cycle types for which the PCD is authorized;
  2. the PCD model, configuration, and intended application;
  3. whether testing occurs in an empty chamber, representative load, or other defined configuration;
  4. the placement and orientation;
  5. the preparation, exposure, and readout conditions;
  6. the PCD identifier and its status within the load record; and
  7. the response to a failed, invalid, or indeterminate result.

Consistent placement and documentation improve comparability, but consistency does not make an unsuitable PCD appropriate. The test configuration must remain relevant to the question being asked and within the device’s stated intended use.

Interpret results with the complete record

Review the PCD result with the sterilizer’s mechanical or electronic record, other required indicators, package or container condition, load configuration, and operator documentation. CDC describes mechanical, chemical, and biological monitoring as complementary elements of sterilization monitoring rather than interchangeable substitutes.[2]

If a PCD result fails or is indeterminate, follow the facility’s approved hold and investigation procedure. As part of that procedure, verify the device identity, usable life, storage and handling, preparation, placement, orientation, exposure conditions, and readout. Review the cycle record, alarms, load arrangement, packaging or container configuration, and recent changes or maintenance as applicable. These are operational investigation steps; the supplied CDC sources support quarantine or retention of items from evaluation cycles until results are acceptable and support representative-product testing after major changes, but they do not prescribe every facility’s detailed failure workflow.[2]

A failed PCD is a process signal requiring evaluation, not a diagnosis of a particular equipment fault. A passing result also does not override a failed mechanical monitor, unacceptable indicator response, wet or damaged packaging, or another documented deviation. Load disposition should follow the facility’s approved procedure and applicable instructions.

Use results to support change evaluation

When packaging, wraps, containers, product arrangements, or load configurations change, reconsider whether the existing monitoring or qualification approach still addresses the intended challenge. CDC recommends testing representative products when major changes are made and retaining items from evaluation cycles until results are acceptable.[2] The exact evaluation method should be defined by applicable equipment and product instructions, recognized standards, validated procedures, and facility policy. The sources provided here do not support a single universal requalification protocol for every change.

Practical checklist

  • Define the monitoring question.
  • Distinguish air-removal testing, small-sterilizer Type 2 PCD use, and product- or load-specific challenge testing.
  • Verify that the PCD is intended for the sterilizer, cycle, and configuration.
  • Follow the manufacturer’s instructions for preparation, placement, readout, storage, and reuse.
  • Use a defined and justified placement and document the surrounding load configuration.
  • Record the PCD identifier and result with the applicable test or load record.
  • Interpret the result with mechanical, chemical, packaging, and load information.
  • Hold and investigate failed or questionable results according to facility procedure.
  • Reconsider the monitoring approach after major product, packaging, or load changes.

Limitations

PCDs are defined challenges, not replicas of every medical device or every load. Their response depends on device design, intended use, cycle conditions, placement, handling, and interpretation. The sources cited here do not establish that one PCD is suitable for all steam sterilizers, gravity-displacement cycles, routine full loads, or product configurations. Facilities should follow current manufacturer instructions, applicable standards, validated procedures, and local requirements.

Educational disclaimer: This article provides general technical education for sterile processing and quality professionals. It is not a substitute for device-specific reprocessing instructions, sterilizer manufacturer instructions, applicable standards, regulatory requirements, or facility policy.

References

  1. Steam Sterilization. U.S. Centers for Disease Control and Prevention. 2023-11-28.
  2. Sterilizing Practices. U.S. Centers for Disease Control and Prevention. 2023-11-28.
  3. ANSI/AAMI/ISO 11140-6:2024 (PDF). Association for the Advancement of Medical Instrumentation. 2024.
  4. Recommendations for Disinfection and Sterilization in Healthcare Facilities: Summary Recommendations. U.S. Centers for Disease Control and Prevention. 2024-06-28.

Educational overview. Follow the applicable product instructions, validated procedures, local regulations and your facility’s approved policies.