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How do you select a correct artificial test soil for cleaning validations

Validating a cleaning procedure starts with selecting an appropriate artificial test soil that is representative of the worst-case challenges that are expected in clinical use for the device being evaluated[1],[2]. Various artificial test soils exist that have been developed to simulate clinically relevant soils such as those that are described in ASTM F3208-20[3], ISO 15883-5[4] as well as in other publications. Because test soil selection will mainly depend on the intended clinical use of the device, there is no one single test soil that is appropriate for all medical devices1,4.  Instead, device manufacturers should consider the contaminants the device will come in contact with as well as the physical characteristics of clinically occurring soiling of the device (such as whether or not blood coagulation will occur).

Both ASTM F3208-201 and ISO 15883-52 contain test soil recipes out of which clinically relevant test soils can be selected. Common test soils include British Standard Soil that can be used to simulate mucous or skin contact, Defibrinated Blood Soil which is a non-coagulating blood soil, or Coagulated Blood which is a coagulating blood-based soil. Additionally, a mixture of test soils may be used when clinically appropriate. For example, for devices that are mainly soiled by mucous but also, to a lesser extent, blood a 90:10 mixture of British Standard Soil and Defibrinated Blood Soil could be selected. These mixtures are often used for Ear, Nose, and Throat (ENT) devices. However, despite the variety of test soils available in guidance documents such as ASTM F3208-201 and ISO 15883-52 there are instances where the test soils outlined in these standards may not represent the clinical soil the device is intended to come in contact with. In those circumstances, a broader approach may be more sufficient and appropriate where a simulated use test soil is created to mimic the contaminants the device would encounter during use. Consequently, any test soil may be used to validate cleaning procedures as long as it can be scientifically justified as reflecting worst-case clinical soil1.

In addition to reflecting the worst-case clinical soil, the artificial test soil that is chosen should quantify at least two clinically relevant soil components for validation testing3. In general, protein residues are considered to be the prime challenge for medical devices and test soils should therefore be protein based4. Other common clinically relevant soil components include hemoglobin and total organic carbon4. Based on the desired markers to be evaluated, test soil selection may need to be adjusted. For example, if hemoglobin is one of the analytes quantified a sufficient percentage of the artificial test soil should be blood-based.

[1] FDA 2015 Reprocessing Medical Devices in Health Care Settings: Validation Methods and Labeling. Guidance for Industry and Food and Drug Administration Staff

[2] AAMI TIR30:2011 A compendium of processes, materials, test methods, and acceptance criteria for cleaning reusable medical devices

[3] ASTM F3208-20 Standard Guide for Selecting Test Soils for Validation of Cleaning Methods for Reusable Medical Devices

[4] ISO 15883-5 Washer-disinfectors Part 5: Test soils and methods for demonstrating cleaning efficacy