When choosing a test method, consideration should be given to a number of factors. These should include, but may not be limited to, the contaminants that the device is expected to come in contact with during actual clinical use (which should be adequately represented in the artificial soil), the test specificity for direct measurement of those constituents, and the sensitivity of the test methods in relation to the proposed cleaning endpoints. Regardless of the test type you choose, visual inspection of both external and internal surfaces should be performed during validation. You should provide a justification for the test types chosen, including any relevant documentation (e.g., FDA-recognized standard, published literature, instructions for use for a commercially-available assay). If your chosen test method deviates in any way from what is described in the provided documentation, then you should identify and justify each deviation. b. Methods Validation You should validate the test methods you choose to measure residual soil. Your documentation of the method should include analytical sensitivity and specificity information, as well as predetermined cleaning endpoints, and should describe appropriate controls. The Agency recommends that your test method include the following controls: § Negative device control – The device should be unsoiled and undergo the same cleaning and extraction as test devices. The amount of residual soil should be at or slightly above the negative sample control. § Positive device control – The device should be soiled with a known amount of soil, but not cleaned, and residual soil extracted. The amount of residual soil should be equivalent to or slightly lower than the amount of soil placed. Soil recovery efficiencies should be calculated and used during the calculations.Contains Nonbinding Recommendations § Negative sample control – “Extraction” is conducted with no device. This sample is used as a blank. § Positive sample control – A known amount of soil (at or slightly above the limit of quantitation) is added to an “extraction” with no device. This control addresses interference of the extraction fluid and extraction method with soil detection. c. Extraction Method 27 Devices should be subjected to a validated method of extraction for recovery of residual soil. The extraction method should be completely described for each device and its recovery efficiency should be determined as part of its validation.
Exhaustive extraction and extraction using a known quantity of soil are commonly used methods for determining recovery efficiency. Extraction should sample all surfaces, including internal surfaces (such as lumens) and mated surfaces. The worst case challenge (most difficult to remove) components of the soil should be addressed in the determination of recovery efficiency testing. You should ensure that the extraction volume used to remove test soil from the device is not so large that the test marker is diluted below the level of detection for the assay. Some device designs include more complex internal structures (e.g., lumens, internal moving parts) that may become soiled during use, but are difficult to access during cleaning and extraction. Hence, cleaning methods, including disassembly, should be designed to access these surfaces.