As I'm sure you are aware the test is based on an indirect measurement of ATP a chemical component in respiration. The test unlike standard swabbing and plating tests measure the presence of protein and from this an assumption is made about the hygienic standard of the surface or sample etc. Standard methods measure the viable numbers of micro-organisms which is a different thing. As a manager and auditors I view these rapid tests as being an excellent indicator of hygienic practices and standards. Even where the result is expressed in RLU's, SLU's as a specific value or number, I still deal with the test as a qualitative test i.e. pass/fail; go/no go. Without knowing the specific process and product risk I can only provide some general advise.
Validation is important. If we take cleaning as the specific area of interest you need to effectively conduct a study or experiment. In other words in the specific context of your process, products and operations you need to know what 100, 200, 300 slu's tells you. What is this saying about your procedures and activities. For example:
1. Take a cleaning procedure as document
2. Confirm through visual observing that the procedure is being carried out as defined. (Steps, chemical make up, usage etc)
3. If not, does the procedure need to be changed or the operator trained? Close this out.
4. Once the above is confirmed, conducted the documented procedure a number of times and conduct standard micro testing for TVC's, pathogens etc.
5. Also conduct the Clean Trace swabbing at the same time under identical conditions, sample points etc
6. Develop a correlation graph between the two sets of results
7. Document all the above and file for inspection/review by your auditors. Show you methodology, results and conclusions clearly.
This will tell you what the SLU results actual reflect and from this you can make validated decisions. I hope this help and it should be sufficient for most auditors.