Where there is a concern that RLU (Relative Light Unit) results are not accurate and these lower than they should be it can raise concerns of interference of the test by residual chemicals remaining on the surface being tested. There can also be concerns related to results being always higher after cleaning again although very uncommon this can be related to effects of some residual chemicals.
Problems that may result in failure to rinse excess cleaning chemicals away during the final stages of a cleaning process, or where there is incorrect preparation of sanitizing chemicals so that they are in a too higher concentration can result in “ quenching “ or elevation of an RLU result. This means the reagents of an UltraSnap / SuperSnap could be damaged and the bioluminescence reaction subsequently inhibited or enhanced. This results in the test being unable to produce the light needed to provide an accurate measure of ATP contamination. In most cases, this will result in a lower RLU result. Or much less common the light produced can be increased and subsequently produce a high RLU result.
For the majority of sanitizers as long as they are prepared to the correct concentration they will have a limited impact on the UltraSnap or SuperSnap test result.
Cleaning chemicals that should be rinsed away or removed during cleaning are most likely to quench the test if remaining on the surface but also in a few cases can increase an RLU value. As part of cleaning, procedure tests should be taken to confirm cleaning chemicals have been removed from a surface or equipment. These include tests for pH or conductivity.
The Hygiena Positive Control test provides a means to check for quenching or reducing of the UltraSnap or SuperSnap results to confirm the RLU results are accurate.
The Positive control vial contains Freeze-dried ATP.
Testing for quenching of an ATP test.
- Control Test – Open a fresh positive control vial.
- Take a new unused UltraSnap or SuperSnap swab and rub the swab bud around the inside of the positive control vial until all the ATP solid has been absorbed onto the swab bud.
- Activate the swab test and then read in the Hygiena luminometer. Record the result.
- Check the result falls in the specification range in the table above. This will confirm the tests and luminometer are functioning correctly.
- Surface quenching test – Take a new unused UltraSnap or SuperSnap and swab the surface where quenching is suspected.
- Open a fresh positive control vial.
- Using the same swab used to sample the surface rub this around the inside of the new positive control vial until all the ATP solid has been absorbed onto the swab.
- Activate the swab test and then read in the Hygiena luminometer.
- Check the percentage difference between the control and test result. (These take into account potential samp0le variation). +/- 30% difference -unlikely there is any significant interference by a sanitiser. > 50% decrease – should be considered a cautionary result and there may be a limited impact on test results but indicates potentially some interference is occurring. >70% difference indicates significant quenching occurring.
- If possible where there are concerns over quenching, rinse the surface and follow from step 4 above to check if there is any reduction in the degree of interference in results prior to rinsing by residues on the surface.
Testing for interference where an increase in RLU results is suspected can be carried simply by dipping the swab tip ( ideally pipetting) to pick up a small amount of the sanitiser in its in-use concentration and then activating and measuring the swab. The result should be no more than 4 RLU.
If possible where routine testing can be taken before sanitizer is applied then this will help reduce the risk of any quenching. Also, this will help prevent the need to reapply sanitizers if recleaning is required.
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