When Are Process Challenge Devices Required?

A sterilizer cycle can meet its displayed time, temperature, pressure, or concentration parameters and still fail to deliver the intended lethality at the hardest-to-sterilize location. That is why the question, when are process challenge devices required, cannot be answered by looking at cycle printouts alone. In regulated environments, the correct answer depends on the sterilization modality, the device or load configuration, applicable standards, validated process parameters, and the instructions for use (IFUs) governing the equipment and monitoring products.

A process challenge device (PCD) is not a paperwork exercise. It is a defined test article designed to present a specified challenge to the sterilization process, typically by placing a biological indicator (BI), chemical indicator (CI), or both in a location that is less accessible to the sterilant than the exterior of a routine load. Used correctly, a PCD provides evidence that the cycle achieved conditions where verification matters most.

When Are Process Challenge Devices Required in Practice?

PCDs are required whenever a governing standard, facility policy, device manufacturer IFU, sterilizer manufacturer IFU, or validated process protocol calls for them. The requirement may apply to routine load monitoring, daily equipment testing, implant-load release, qualification work, or investigation after a process failure.

The central compliance principle is straightforward: use the monitoring method and frequency specified for the process you are running. Do not substitute a convenient indicator or generic test pack for a PCD that has been qualified or specified for the cycle. A PCD must be compatible with the modality, cycle type, and intended challenge.

In healthcare steam sterilization, PCD use commonly appears in several distinct situations. Dynamic-air-removal steam sterilizers require an air-removal test before processing the first load of the day the sterilizer is used. This test is often performed with a Bowie-Dick-type test pack or an equivalent device qualified for that purpose. Its function is to assess air removal and steam penetration, not to release a clinical load.

Routine BI monitoring is another situation. Healthcare facilities generally establish a defined frequency for biological monitoring, often at least weekly and frequently more often based on their risk assessment, workflow, policy, and governing guidance. The BI should be placed in a PCD or representative challenge package that presents a meaningful test of the process. A BI sitting loosely on a tray does not provide the same evidence as a properly configured PCD.

For implant loads, the expectation is more demanding. A BI PCD is commonly run with every implant load, and the load should be quarantined until the BI result is known unless an emergency release process is justified, documented, and controlled under facility policy. Patient safety, traceability, and the consequences of a failed result justify that higher level of assurance.

PCD Requirements Vary by Modality

The phrase “required” can create a false impression that one PCD design works across every sterilization process. It does not. Steam, ethylene oxide (EO), vaporized hydrogen peroxide (VH2O2), dry heat, formaldehyde, and radiation processes expose materials to fundamentally different sterilizing conditions. The challenge device must reflect the mechanism being evaluated.

Steam Sterilization

For steam, air removal and steam contact are often the critical variables. A PCD may simulate a wrapped instrument set, a lumened load, or another defined challenge consistent with the sterilizer cycle and processed devices. Pre-vacuum cycles, gravity cycles, immediate-use cycles, and specialty cycles can require different monitoring approaches.

The cycle’s exposure temperature and time matter, but so does the load. Dense metal sets, rigid containers, textiles, and complex instruments do not behave identically. If the facility processes a difficult load configuration, its monitoring plan should address that configuration rather than relying on the least challenging tray in the department.

Ethylene Oxide Sterilization

EO sterilization requires control of parameters such as gas concentration, temperature, humidity, exposure time, and aeration. PCDs used for EO must be validated for the EO process and placed where they can assess the intended load challenge. Because EO often sterilizes complex medical devices and packaging systems, the PCD location and construction deserve careful attention.

For many EO operations, BI PCDs are incorporated into routine load monitoring because they provide direct evidence of microbial lethality under defined conditions. The exact frequency and release criteria should come from the validated process, quality system procedures, applicable consensus standards, and product IFUs.

Vaporized Hydrogen Peroxide and Other Low-Temperature Processes

Low-temperature sterilization presents its own set of limitations. Device compatibility, lumen dimensions, material composition, load arrangement, and cycle selection can all affect sterilant delivery. A PCD intended for VH2O2 should not be assumed suitable for steam or EO simply because it contains a BI.

This is particularly relevant when processing devices with long or narrow lumens. The most challenging location may be within the device pathway, a dedicated lumen PCD, or another configuration specified by the device and sterilizer manufacturers. If the IFUs prohibit a cycle for a device or load type, no PCD result can make that cycle acceptable.

Qualification, Requalification, and Failure Investigations

PCDs become especially critical when a sterilization process is being established or changed. During process development and validation, they can help characterize whether the intended cycle delivers sterilant effectively to the defined worst-case challenge. In these settings, the PCD is part of a larger protocol that may include physical measurements, BIs, CIs, load configuration studies, and documented acceptance criteria.

Requalification may be necessary after material changes, packaging changes, sterilizer relocation, major repair, software updates, cycle changes, or the introduction of a new device family. The scope depends on the change-control assessment. A minor adjustment may require targeted confirmation, while a change affecting cycle performance or the worst-case load can require a more extensive study.

After a positive BI, failed air-removal test, out-of-spec physical parameter, or unexplained CI result, PCDs may also be used as part of the investigation and corrective action process. The goal is not to run a single retest and move on. The team must determine whether the result reflects a monitoring error, PCD assembly error, loading issue, equipment malfunction, utility problem, or broader process failure.

A defensible investigation preserves the failed indicator, cycle records, load information, maintenance history, and corrective actions. Retesting may be appropriate, but it does not erase the original nonconformance.

Selecting the Right PCD for the Requirement

A compliant PCD program begins with a written rationale. Identify the modality and cycle, the applicable IFUs, the load or device challenge, the indicator type, the placement location, the incubation or interpretation method, and the release decision tied to the result. This documentation is what allows a facility or manufacturer to explain its approach during an audit.

Avoid two common errors. First, do not confuse an external process indicator with a PCD. External indicators show that a package was exposed to a process, but they do not demonstrate sterilant penetration to an internal challenge location. Second, do not assume the most difficult-looking PCD is automatically the best one. An artificially severe device that does not represent the validated process can produce misleading results and unnecessary operational disruption.

The right device is the one that is specified, appropriate, and supported by evidence. Product documentation should clearly define intended use, cycle compatibility, storage requirements, performance characteristics, and interpretation criteria. For regulated users, lot traceability and documentation such as technical data sheets, certificates of analysis, and safety information are equally part of the assurance package.

Build a Monitoring Program That Holds Up

For sterilization program managers and quality teams, the practical decision is not whether to use PCDs whenever possible. It is whether each PCD is being used for the correct purpose and under a controlled procedure. Review monitoring plans against current standards, equipment IFUs, medical device IFUs, and internal quality requirements. Then verify that staff training, documentation, incubator controls, and load-release procedures match what the plan says.

True Indicating supports organizations that need monitoring products and technical guidance aligned to specific modalities, cycle conditions, and regulatory expectations. Where standard solutions do not fit the process, a tailored challenge device and verification strategy may be the more defensible path.

Don’t leave a high-consequence sterilization decision to a generic test pack or an assumed requirement. Define the real process challenge, document the basis for your PCD selection, and make every monitoring result meaningful.