Enzymatic comparative test for glutaraldehyde residues on flexible endoscopes

IGF 18893 N

The majority of flexible endoscopes is reprocessed automatically using washer-/disinfectors. As these instruments are made of temperature sensitive materials, they cannot be reprocessed using established thermal disinfection procedures. Therefore, they have to be reprocessed chemo-thermally using chemical disinfectants. The prevalent disinfectant component used in Germany is glutaraldehyde (GA).

Endoscopes are applied invasively (inside the body) and get in contact with mucous membranes. Thus, residues of the highly toxic GA on the endoscope surface can cause severe inflammatory reactions, such as GA-associated colitis. Therefore, the maximum limit value for GA was set to 1.5 µg/cm2 instrument surface. The safety of reprocessed endoscopes has to be assured by the operators of the devices or the reprocessing personnel, respectively.

Tests have to be applied to assure patients safety with respect to the applied reprocessing procedures and the particular devices. Test procedures like the assessment of biocompatibility (according to DIN EN ISO 10993-5) and very complex instrumental analytics to quantify GA are highly intricate. Both test methods have to be commissioned to external test laboratories and results are not available for the routine clearance of the reprocessed instruments. Within this research project, the wfk-institute developed an enzyme-based test for the presence of GA on surfaces.

It can be used as a final product control or in combination with test material sections as a process control. The new test method allows assessment of critical residual GA levels (1.5 µg/cm2) on the surfaces of endoscopes within 10 min. The rapid test is easy to apply and utilizes an enzyme-substrate-combination, which is bound to a carrier-membrane in the form of a thin sheet (test strip). The carrier-membrane is applied on defined areas of the endoscope surface and is incubated for exactly 10 minutes.

In the presence of critical GA-residues, a colour reaction from blue/green to colourless occurs. The system was modified so that discolouration process starts in the presence of residual GA-concentrations of 1.0 – 1.5 µg/cm2. GA-concentrations above 1.5 µg/cm2 lead to a complete discolouration and the carrier-membrane turns white. Due to the easy handling and evaluation and in combination with the fast reaction time, which provides results in a time-span of 10 minutes, the test can be perfectly integrated into the established work-flow of endoscope-reprocessing and enables routine controls.

Usability and function of the test were assessed under practical conditions using reprocessed real instruments at three different hospitals in NRW, Germany. A total of 11 endoscopes (bronchoscopes, gastroscopes, duodenoscopes, coloscopes) were tested. At 6 out of the 11 instruments, the test revealed the presence of GA-residues >1.5 µg/cm2 on at least one examined area (each time, the distal end and the insertion tube were tested) of the respective endoscope.

The results of this first random testing stress the practical importance of the developed rapid test in order to improve hygiene safety during reprocessing of critical medical devices.
Professional reprocessing service providers, which operate in more than 1950 hospitals and numberless doctor’s offices by reprocessing thermosensitive medical devices using chemo-thermal processes, will profit from the research results.

Approximately 8 million endoscopes are reprocessed in Germany each year. In the future, these instruments can be monitored regarding the required absence of GA residues using the new enzyme-based rapid test method, considerably improving the safety of patients, operators and third parties.

The research report is available on request from FRT.

The IGF-pro­ject 18893 N of the re­search as­so­ci­a­tion Europäische Forschungs­ge­mein­schaft Reini­gungs- und Hy­gien­etech­nolo­gie e.V., Cam­pus Ficht­en­hain 11, 47807 Krefeld, was sup­port­ed with­in the fund­ing pro­gram „In­dus­trielle Gemein­schafts­forschung und -en­twick­lung (IGF)“ by the Fed­er­al Min­istry of Eco­nom­ic Af­fairs and Cli­mate Ac­tion due to a de­ci­sion of the Ger­man Par­lia­ment.