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Four Important Things to Know About Particulate Testing and Medical Devices

Particulate testing is required for medical devices to ensure patient safety, but there isn’t a lot of guidance available for how to perform particulate testing or what limits are appropriate.  Here are four important things you need to know about particulate testing on medical devices.

First, while there are some device-specific standards, such as ISO 8536-7 Infusion equipment for medical use – Part 4: Infusion sets for single use, gravity feed, there isn’t an overall test standard for medical-device particulate testing.  Particulate tests are based on analyzing a liquid sample, either by placing that sample in a light obscuration (LO) particulate counter, which generates a particulate count, or by using membrane filtration, which captures the particles on a filter and requires manual counting of the particles using a microscope.  As such, to perform a particulate test, the device is usually extracted or washed to remove the particulates, and then the particulates are placed into a solution for analysis.  This liquid extract is then tested using USP <788> Particulate Matter in Injections. Although it is specific for injectables, it is the most commonly used standard for devices.

Second, the manner in which the device is extracted can have a significant impact on the reported particulate count.  The extraction method should be documented so it can be performed the same way with each test for consistency.  Steps should be included to minimize potential contamination during the extraction process, and careful thought should be taken to ensure the extraction is representative of clinical use.  The amount of extract fluid should also be thoughtfully selected and should represent clinical use.

Third, particulate limits should be set for the device that are meaningful and appropriate.  Setting a limit too high could allow potentially harmful product to be released to market and setting a limit too low could result in failed product that is actually safe to use.  While there are limits in the standards, those limits may not actually be appropriate for your device.  Blindly adopting a limit value created for injectables when your product is a device could be problematic, since those two may not be in the same risk category.

Fourth, there is no defined sample-size number for particulate testing on medical devices.  USP <788> says, “The number of test specimens must be adequate to provide a statistically sound assessment.”  USP <788> does mention a sample size of 10 units or fewer using an appropriate sampling plan. However, this standard is for production pharmaceuticals that are produced in large homogenous batches and then filled in individual containers.   A sample size of 10 may not be appropriate for medical devices, which are produced individually and subject to more variation in particulate counts.  A sampling-size justification (how many to sample) and sampling plan (when and where to sample) should be developed based on risk, incorporating a statistically significant rationale.

Particulate testing on medical devices can be challenging, due to the lack of a defined test method.  However, keeping these four points in mind, these challenges can be overcome.  The unknown and undefined aspects of particulate testing can be defined by each manufacturer using the same principles that are common to other types of tests performed on medical devices.   If this task seems overwhelming, consider partnering with the Expert Advisory Services (EAS) group at Nelson Labs.  Our experts are a great resource and can assist you with creating appropriate extraction methods, selecting and setting particulate limits, and completing sample-size justifications or any other task.