Issue m³ 01 · 13 October 2026 · Edited by Alessandro Ligugnana
m³ 01 · Routine monitoring and trending
ONE CUBIC METRE is about environmental monitoring in pharmaceutical cleanrooms, one cubic metre of air at a time. Each issue picks one subject, clears it up without jargon and finishes with the line to note on the record. It is written for the people who then have to get that idea across to the staff on the floor. If it cannot be read aloud without too many footnotes, it is not ready yet. Each issue is published here and on LinkedIn on the same day.
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The sentence
“Monitoring procedures should define the approach to trending.”
EU GMP Annex 1, Manufacture of Sterile Medicinal Products, C(2022) 5938 final, 22 August 2022, §9.11.
The official text of the standard is binding.
What it means
Monitoring is not a check you do once and file away. Results have to be put in a series, so you can see whether things are stable, getting worse or getting better. How this is done has to be written down beforehand, in the procedures: which data are reviewed, how often and what counts as a signal.
A single value says little: it can be a spike, an anomaly or a lucky moment. The series tells you whether the process stays under control over time. This applies to particles and to microorganisms.
The same paragraph lists what trends should include as a minimum: increasing numbers of excursions from action limits or alert levels, consecutive excursions from alert levels, regular but isolated excursions from action limits that may have a common cause, and changes in microbial flora type and numbers and in the predominance of specific organisms.
Trending does not mean printing a chart once a year. It means looking at the data over time, recognising shifts and acting when the trend changes. Without it, an out-of-limit result stays an isolated event. With it, it becomes a signal you can read and explain.
An example
In a grade C room where solutions to be filtered are prepared, particle counts are taken every day at the critical points and once a week at the others.
For three weeks the values stay below the alert level. Then, for five days in a row, the average at the same point rises by 40%, still below the action limit.
Without trending, those results are filed as compliant. With trending, the pattern shows, and it can be investigated before the value crosses the limit: a filter losing efficiency, a door that does not close properly, a change in how people or materials move. No single result would have triggered anything. The series did.
The same reasoning applies to microbiological sampling. An isolated result of 1 CFU can be noise. Five consecutive results of 1 CFU at the same point, after weeks with no growth, are a signal.
On the record
Monitoring performed at the defined frequency. Results trended per procedure.
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