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Many High Level Disinfectants (HLDs) are intended to be re-used, meaning that the same fluid disinfects several critical or semi-critical medical instruments each day for weeks.

Accordingly, FDA requires re-usable products to be “stressed” to worst-case conditions prior to efficacy testing.

The re-use test is a critical part of any HLD 510k submission for re-usable products. It generates “worst-case” product for use in several required efficacy tests, such as the AOAC Sporicidal Activity of Disinfectants Method, and it provides an estimation of the length of time the product will withstand use in the clinic before it must be replaced.

For a typical re-use test, the product is stressed in three ways. First, it is stressed by aging to the end of its expected shelf life. Second, it is stressed by exposure to clinically-relevant microorganisms and a broad array of animal proteins. Laboratory staff expose the HLD to biological matter daily, which depletes the activity of the active ingredient. Lastly, the product is stressed by dilution. Several times each day through the course of the re-use study, the HLD is exposed to corrugated respiratory care equipment. At intervals, the respiratory equipment is removed, enzymatically cleaned, rinsed, and placed back into basin with the HLD. During this process, the respiratory care equipment retains either HLD or rinse water, depending on whether it is being removed from or returned to the basin containing the HLD.

The active ingredient concentration of the HLD is monitored during the re-use test, typically by chemical titration. Once the concentration approaches the lowest concentration of active ingredient required for the HLD to remain adequately microbicidal (called the MRC, or minimum recommended concentration), the study is terminated and the days of re-use tolerated by the HLD is reported.

MRC concentrations vary depending on the active ingredient. Examples of known MRC values for several active ingredients are presented below:

  • Ortho-phthalaldehyde – 0.3%
  • Glutaraldehyde – 1.5%
  • Peracetic Acid – 2.0%

The re-use period can last anywhere from 5 to 28 days depending on the stability of the active ingredient, its resistance to organic matter, and the exposure temperature of the study, which is sometimes elevated to match exposure conditions in automated endoscope reprocessors.

The re-use test provides an excellent indication of expected HLD use-life. To be extra safe, active ingredient levels are also checked during clinical use. Re-usable HLD products are often sold with validated chemical test strips to quickly measure active ingredient concentration. These test strips are specific for the HLD product and are calibrated to show approximately 50% failure at the MRC and 100% failure below the MRC.

If your company has questions about HLD testing, Microchem is here to help.