Why Reusable Lumen Instruments Are So Hard to Clean

Cleaning reusable surgical instruments is the step that makes everything after it possible. Disinfection and sterilization only work if the instrument is clean first, and yet cleaning is also the step most exposed to human variability, tight timelines, and instrument designs that fight back. A 2025 study of suction-type metal lumen instruments put hard numbers on just how often that step falls short, and the results are worth the attention of anyone who runs a sterile processing operation.

 

This article breaks down what the study found, why lumen instruments are such a difficult case, and what it means for how facilities think about reprocessing.

What the Study Looked At

Researchers Yuqi Wu and Li Li examined 190 reused suction-type metal lumen instruments collected from the central sterile supply department (CSSD) of a grade A tertiary hospital between September 2023 and March 2024. These are the narrow hollow instruments used to suction blood, body fluids, and pus during surgery. Because they work by negative pressure, contaminants get pulled into the lumen and cling to the inner walls, where they are far harder to reach than anything on the outer surface.

 

The team checked each instrument for cleaning quality using three different methods and compared the results: a 5x magnifier visual inspection with a light source, an occult blood (OB) reagent test that detects serum residue, and ATP bioluminescence testing, which measures organic and microbial residue and is widely used in UK and US hospitals for rapid cleanliness monitoring.

The Finding That Should Give Any CSSD Pause

Here is the headline result. When cleaning quality was judged by ATP bioluminescence, 75 of the 190 instruments, or 39.5%, failed. Nearly four in ten instruments that had already been through the cleaning process still carried enough residue to be flagged as inadequately cleaned.

 

That figure is not an outlier. The authors point to an earlier study by Li Aiqin and colleagues that found suction-type lumen instruments had the highest unqualified cleaning rate, 44.4%, of any reused instrument category in the CSSD. Lumen instruments are, in other words, a known weak point.

Why Visual Inspection Alone Is Not Enough

The most striking part of the study is how much the answer changed depending on how you measured it. The three methods produced very different pass rates:

 

• 5x magnifier visual inspection: 94.2% passed
• Occult blood reagent test: 72.6% passed
• ATP bioluminescence: 60.5% passed

 

The difference between the methods was statistically significant. Look only at what the eye can see through a magnifier, and better than nine in ten instruments look clean. Test for actual organic and microbial residue inside the lumen, and that number drops by more than thirty points. A curved, narrow lumen simply does not give up its secrets to visual inspection, and the residue that visual checks miss is exactly the kind that feeds bacterial growth and biofilm.

 

This is the practical takeaway: a lumen instrument that passes a visual check has not necessarily been cleaned to the standard that safe sterilization requires.

The Five Things That Made Cleaning Fail

The researchers ran a regression analysis to find which factors independently drove poor cleaning results. Five stood out, and every one of them is a process variable a facility can influence:

 

1. Time between recycling and cleaning. Waiting 20 minutes or more before cleaning was a significant risk factor. In this study, 38.9% of instruments waited that long or longer, with one waiting 96 minutes. The longer contaminants sit and dry inside a lumen, the harder they are to remove.
2. Level of contamination. Heavily soiled instruments failed at a significantly higher rate than lightly soiled ones. Dense organic matter shields microbes and resists both physical and chemical cleaning.
3. Pretreatment soaking time. A soak of 2 minutes or less was a risk factor. Instruments with dried-on residue need to soak in a neutral multi-enzyme solution long enough to loosen the contaminants, with the authors pointing to a 2 to 10 minute range.
4. Manual versus machine cleaning. Manual cleaning produced significantly more failures than machine cleaning. The human eye cannot reliably find small amounts of residue spread through a lumen, while purpose-built injection washers deliver consistent pressure, temperature, and flushing.
5. Visible residue after pretreatment. When bloodstains or dirt remained after pretreatment, cleaning quality dropped. Pretreatment is meant to set up a clean result, and skipping or rushing it carries forward.

 

None of these are exotic failures. They are ordinary pressures of a busy department, and any one of them can leave residue behind.

Why Lumens Are the Hard Case

The trouble with a hollow instrument is not only cleaning, it is what inadequate cleaning does to the steps that follow. When organic residue is left inside a lumen, it becomes food for bacteria and a foothold for biofilm. Research cited in the study found that leftover organic and inorganic matter significantly reduces the effectiveness of sterilization methods, including autoclaving, ethylene oxide, and hydrogen peroxide, because residue forms a protective layer that keeps the sterilizing agent from reaching the microbes underneath.

 

Lumens add a second problem: air. Sterilizing agents have to physically contact every surface to work, and it is difficult to clear air out of a long, narrow channel. Where air stays trapped, the sterilant may never reach parts of the inner wall. So a lumen that was not fully cleaned, and may not be fully reached during sterilization, is a genuine gap, and the study frames inadequate cleaning as a driver of increased infection risk for the next patient.

 

It is worth being precise about scope. This was a single-center study of 190 instruments, and the authors note limitations including the small sample and possible selection bias. It is a snapshot, not the last word. But it aligns with a broader body of evidence that hollow and complex instruments are among the hardest to reprocess reliably.

What This Means for Reprocessing Decisions

The honest reading of this data is not that CSSDs are failing. It is that reliable cleaning of lumen instruments depends on a chain of steps going right every time, under real-world time and staffing pressure, on instruments whose design works against inspection. Strong departments manage that chain well through training, machine cleaning, prompt pretreatment, and verification methods like ATP that catch what the eye cannot. Those are the right investments, and the study points directly to them.

 

Single-use instruments enter the conversation at a different point. A single-use lumen or suction instrument arrives new and unused for one procedure, then is discarded, so it never passes through the reprocessing cycle where this variability lives. That removes cleaning and cleaning verification as a variable for that specific instrument. It does not replace a facility’s reprocessing program, it is not a claim about sterility on its own, and it is not a substitute for sound sterile processing practice. What it offers is one fewer hard-to-clean item moving through a department that, as this study shows, already carries a real reprocessing burden on exactly these designs.

 

The useful question is not whether reusable or single-use is better in the abstract. It is which specific instruments in your trays are the hardest to clean and verify, and whether a single-use option for those items would take pressure off the process where it is most likely to break.

Frequently Asked Questions

How often do reusable lumen instruments fail cleaning checks? In this 2025 study of 190 suction-type metal lumen instruments, 39.5% failed when tested by ATP bioluminescence. A separate study cited by the authors found an unqualified cleaning rate of 44.4% for suction-type lumen instruments, the highest of any reused instrument category.

 

Why does visual inspection miss dirty instruments? Visual inspection cannot see inside long, narrow, curved lumens. In the study, 94.2% of instruments passed visual inspection but only 60.5% passed ATP testing, which detects organic and microbial residue the eye cannot.

 

Why is cleaning so important before sterilization? Cleaning is a prerequisite for effective sterilization. Leftover organic residue can form a protective layer over microbes and reduce the effectiveness of autoclaving, ethylene oxide, and hydrogen peroxide, and trapped air in a lumen can keep the sterilant from reaching the inner surface.

 

What makes lumen instruments harder to clean? Suction-type instruments pull blood and body fluids into the lumen by negative pressure, so residue clings to inner walls that are difficult to reach, inspect, and flush. Time delays, heavy soiling, short soak times, manual cleaning, and leftover residue after pretreatment all worsen the result.

The Bottom Line

The data makes a clear point. Reusable lumen instruments are genuinely hard to clean, the failure rate is high enough to matter, and visual inspection alone gives a falsely reassuring picture. For most instruments, the answer is a stronger reprocessing chain. For the hardest-to-clean designs, it is worth asking whether a single-use option would remove a point of variability rather than manage it.

 

If your team is mapping which instruments in your trays create the most reprocessing risk and where single-use options might help, we are glad to talk it through.

 

Source: Wu Y, Li L. An investigation into cleaning quality of suction-type metal lumen instruments: a cross-sectional study. Sci Rep. 2025;15:2492. https://doi.org/10.1038/s41598-024-83215-8