Cleaning is the most important step in the entire reprocessing cycle. No sterilisation process, however advanced, can reliably render an instrument safe if organic soil remains on its surface. The question that CSSD professionals must therefore ask is: how do we know when an instrument is truly clean? For many years, ATP (Adenosine Triphosphate) bioluminescence testing has been promoted as the answer. The evidence, however, strongly suggests that protein residue testing is a far more appropriate and reliable method for the CSSD environment [3]
Understanding ATP Testing and Its Limitations
ATP testing was originally developed for the food and beverage industry, where it serves as an effective proxy for microbial contamination on food-contact surfaces. The test works by detecting ATP — the universal energy molecule found in all living cells — using a bioluminescent reaction that produces a measurable light signal. The principle is sound for food hygiene, but the CSSD environment presents several factors that fundamentally undermine its reliability.
First, ATP is a highly unstable molecule that is rapidly hydrolysed by the very conditions present in hospital washer-disinfectors: high temperatures, alkaline detergents, and enzymatic cleaners [3]. A passing ATP result after a wash cycle may simply mean that the ATP molecule has been chemically destroyed, not that the instrument is free of organic contamination. Second, some commercial ATP systems have been shown to fail to lyse certain bacterial cell types, meaning the ATP within those cells is never released for detection [3]. Third, ATP is entirely absent from viruses and prions — the protein-based infectious agents responsible for transmissible spongiform encephalopathies such as variant Creutzfeldt-Jakob disease [3]. An ATP test will never detect a prion-contaminated instrument, regardless of the level of contamination.
The Case for Protein Residue Testing
Proteins represent the most challenging and clinically significant organic soils found on surgical
instruments. Blood and tissue residues contain a complex mixture of cell types and free proteins, and it is the coagulated, heat-fixed proteins that are most resistant to removal during the cleaning process [3]. When proteins remain on an instrument surface, they can physically shield microorganisms from the sterilising agent, creating a protective biofilm that renders sterilisation unreliable. Protein residue testing directly measures this critical contaminant. Unlike ATP, proteins are stable molecules that are not degraded by the cleaning process itself; if they remain after washing, the test will detect them. This makes protein testing a direct and accurate measure of cleaning efficacy. The clinical significance of this distinction has been recognised at the highest regulatory levels. The UK Department of Health’s Health Technical Memorandum 01-01 (HTM 01-01) sets specific quantitative limits on residual protein — measured in micrograms — as the benchmark for a “clean” instrument [3].
About Proline Medical Pty Ltd
Proline Medical is an Australian-owned company headquartered in Lawnton, Queensland, dedicated to enhancing patient safety through high-quality, innovative solutions for healthcare professionals. As a local manufacturer of SSMMS Sterilisation Wrap and a leading supplier of healthcare cleaning chemistries, Proline Medical serves Central Sterilising Supply Departments, Endoscopy Departments, Operating Theatres, Hospital Wards, and Oral Health facilities across Australia.
Our services include:
Performance Qualification Testing — Comprehensive PQ and re-qualification services aligned with AS5369:2023 and relevant ISO and EN standards, covering all washer-disinfectors including bedpan washers and flusher sanitisers.
Water Testing — Specialised water quality analysis services targeting the requirements of AS5369:2023 Tables 7.2, 7.3, and 7.4.
Decontamination and Sterilisation Consumables — A comprehensive range of cleaning and disinfection chemistries, sterilisation laminates, quality assurance consumables, and air/water cleaning guns.
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