Fluorescent markers vs ATP testing
Fluorescent markers show whether a marked surface was wiped. ATP testing measures organic residue on a surface, as a reading in relative light units on one meter. They answer different questions, so they often disagree on the same rooms. Record which method produced each result, and how it was judged.
What a fluorescent marker shows
A gel or powder that is invisible in normal light is dabbed on high-touch surfaces before the clean. Afterward, someone checks each spot with a UV light. A removed mark means the surface was wiped. The result is a count: marks removed out of marks placed.
A marker shows how thorough the wiping was. It says nothing about residue or microbes, and only about the spots that were marked. Vary where the marks go, so the check stays a fair sample of the room.
What ATP testing measures
ATP is a molecule found in living cells and in organic residue. A swab of one surface goes into a meter, which measures the light from a reaction with the ATP it finds and reports a number in relative light units (RLU).
An ATP reading gives a number for one surface at one moment. It doesn't identify what the residue is, and the number belongs to the meter model that produced it.
Why they disagree
Fluorescent markers rated 76% of surfaces clean; ATP rated 45%, across 100 terminal-cleaned rooms.
The two methods measure different things, which is why the method has to be stored with every result. Across the same 500 surfaces in 100 rooms, 378 (76%) were judged clean by fluorescent marker, 384 (77%) by aerobic colony count, and 225 (45%) by ATP. Surfaces the marker called clean were significantly less likely to pass the culture and ATP assays.
Neither method is the correct one. A surface can be wiped and still carry residue, and the two methods look at different things. That is why a result means little without its method.
Which should you use?
Either, or both: markers to check how thoroughly surfaces were wiped, ATP to check residue on surfaces you choose. Whichever you use, use it the same way every time, so this month's results can be compared with last month's. Don't pool marker results and ATP readings into one score.
How to record results so they hold up
For every result, keep:
- The method
- For markers: how many surfaces were marked, and how many marks were removed
- For ATP: the surface, the reading, the meter model, and the threshold your facility set for that model
- Who tested, and when
- Which room's record the result belongs to
- A photo, where you can take one
ATP readings in relative light units are not comparable across meter brands.
Different brands produce widely different log10 RLU values for the same fixed quantity of ATP, so an acceptance threshold belongs to one device model and cannot be carried across to another. Repeatability is also poor near the commonly quoted 100 RLU mark, and published cutoffs in the literature range from 100 to 500 RLU.
Sources
- Boyce et al., Comparison of fluorescent marker systems with 2 quantitative methods of assessing terminal cleaning practices. Infection Control and Hospital Epidemiology, 2011.
- The comparative performance of three brands of portable ATP bioluminometer intended for use in hospital infection control. Healthcare Infection (CSIRO Publishing), 2012.
This guide is general information, not clinical advice. Your facility's protocol and your product labels govern how rooms are cleaned.
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See how one terminal clean becomes one record.
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