What is Worst-case

As a lab specializing in the medical device industry, “worst-case” is a term frequently heard from our clients. It’s also sprinkled throughout guidance documents, such as ISO 11607, and is included in most protocols we write or review. It’s a term that seems straightforward on the surface, but what does it really mean for you and your product when it comes to testing?

If your product line consists of a single item packaged in a single configuration, defining the worst-case packaging system is pretty straightforward. What if you offer a few different sizes or versions of a medical device, or what if you offer it in differing quantities (i.e a single unit and a ten-pack kit)? Having even a few device or packaging variants within your product line can quickly muddy the waters and leave folks scratching their heads about what really needs to be tested. Fortunately, ISO 11607 gives us some guidance in this situation:

“When similar medical devices use the same packaging system, a rationale for establishing similarities and identifying the worst-case configuration shall be documented. As a minimum, the worst-case configuration shall be used to determine compliance with this part of ISO 11607.”

Essentially, we’re being told that we don’t have to test every variant of product line. We can identify “families” or “groups” and then determine what is truly worst-case. We also need to understand that worst-case doesn’t apply only to the device or package. We need to consider the worst-case processes, too.

This list looks at the most common factors and processes to be considered when determining “worst-case”:

Worst Case Factors and Processes

Mass. The heaviest items are typically considered worst case. A heavy product may be prone to cracking a tray or pushing through a seal when dropped.

Size. The largest and/or smallest are typically considered worst case. If multiple products share a tray, for example, the small product may be more likely to shift and move within the tray, while the largest may strain seals.

Geometry. Sharp edges typically provide the worst-case geometry as they can poke through flexible materials.

Package. Larger pouches have more seal area and are typically considered worst-case over smaller pouches with less sealing area. Larger pouches also possess more surface area which provide a larger canvas for abrasion and flex cracking during transit.

Sealing/forming. Low parameters for sealing are often considered worst case as they typically produce the lowest seal strength. Likewise, high parameters may be worst case in forming applications as they typically produce the thinnest package corners.

Configuration. The package containing the most units is typically considered worst-case. More devices typically mean more weight. The added weight is more likely to cause damage than in a package containing fewer samples and weighing less as the contents inside have to bear the weight of the components above them.

Sterilization. 2X sterilization is typically used as worst-case. More processing increases the chance of the package system being negatively affected by the sterilization process.

If Only It Was that Easy

Cruel as it may seem, there is no 100 percent, clear-cut way to define worst case. Instead, by looking objectively at your product and package system as a whole, you can determine which of the criteria presented here best apply to your situation. We often see multiple packaging configurations arrive for testing, when a single worst-case device or configuration cannot be identified. We also see companies take a “bookend” approach, testing the largest and smallest configurations. This approach assumes that if the smallest and largest items are tested successfully, then everything in between should be acceptable, too. Both approaches allow informed conclusions and direction on how to proceed.

At the end of the day, defining worst-case is an exercise in logic and sound judgment. If you need help defining worst-case devices, packages, or processes we’re here to help. Let working with PCL be your best-case scenario for your next project.