A filter tester is not one instrument doing one job. It's a method set — five of them — packaged around your filtration program. Most buying mistakes happen at the spec sheet, before anyone touches an instrument, and they're expensive to fix afterwards.
You're buying methods, not a box
A sterilizing-grade filter does one job: hold back everything that's alive while your product passes through. The FDA's 2004 guidance on sterile drug products produced by aseptic processing defines it plainly — a filter that, when appropriately validated, removes all microorganisms from the fluid stream and produces a sterile effluent. The word doing the heavy lifting is "validated."
Validation has to be proven, not assumed. And the proof is integrity testing. So when a budget line says "filter tester," what you're actually ordering is a set of methods wrapped in an instrument. The box matters. The method coverage matters more. Scope the gap first, buy second — in that order, the purchase is usually fine.
Five methods, five different questions
The USP <43> and EP 11.0 set has five working methods. Each one asks a different question about the same membrane:
Bubble point — the pressure at which the first continuous stream of air flows through the wetted membrane. It flags the largest flow-through pore. Fast, non-destructive, repeatable. This is the check you run on every fill.
Diffusive flow — how much air passes through the wetted membrane under a set pressure. It's sensitive to small changes in membrane condition, which is why it carries a lot of the post-use work.
Dry bubble — run on the dry filter, typically at qualification. The pressure where air first flows is the as-supplied condition, and it becomes the reference everything else gets compared against.
Pressure hold — does the filter hold a set pressure over time? A slow drop is a leak, and the slope of the drop is the information.
Vacuum decay — the decay method. It answers a different physical question than the pressure-side methods and covers configurations they can't reach.
Your procedure decides which question gets asked, and when. The instrument has to be able to ask all five — or you'll end up buying a second one to cover the gap, at double the price of the first.
The 2022 Annex 1 rewrite is still landing
EU GMP Annex 1 has been revised repeatedly — 1997, 2008, 2022 — and the 2022 revision, due for implementation in 2023, did real work on the PUPSIT language.
Under the 2008 text, the filter was to be verified before use and confirmed immediately after use by an appropriate method such as bubble point, diffusive flow or pressure hold. The time taken to filter a known volume, and the pressure difference across the filter, got determined during validation — and any significant difference during routine manufacturing was noted and investigated. Results went into the batch record.
The 2022 text sharpens both ends. Verify integrity before use, to catch damage and loss of integrity caused by filter preparation. Then — and this is the part that changes procurement — a sterilising-grade filter used to sterilise a fluid stream gets a non-destructive integrity test post-use.
It also concedes the real-world problem. PUPSIT may not always be possible after sterilisation, for example when filtering very small volumes of solution. In those cases you document a thorough risk assessment and implement controls that mitigate the non-sterility risk. The alternative approach is legitimate, but only with that paper trail.
What it means for the spec sheet: post-use has to be non-destructive, which rules out methods that consume or alter the filter. And programs are moving toward one instrument running the full set instead of a specialist box per method. If your spec doesn't say "post-use, non-destructive," that's a gap you'll discover at the line, not in the lab.
What to check before you sign
Run the checklist top to bottom. Each item has failed a purchase before.
Method coverage. All five, or a documented justification for each one you're not running. "We only do bubble point" is a statement about your procedure, not a reason to buy a single-method instrument — procedures change, and the filter on the next line might not.
Measurement system. The sensitive measurement is the product. The Integtest V6.5, for instance, is specified around a very sensitive measurement system, with conditions developed in accordance with GAMP guidelines. That's the line you want to see in the documentation, because it tells you how the instrument behaves at the edge of its range — and that's where integrity testing lives.
Records. Full compliance with 21 CFR Part 11 is the table stake in a GMP shop. Check how records leave the instrument — USB, PC, whatever your LIMS actually speaks. An instrument that keeps years of history but only talks to itself is a filing cabinet, not a data source. The V6.5 stores more than 15,000 sets of historical records on board, unlimited in structure.
Qualification documentation. IQ/OQ/PQ should ship with the instrument. If it's a separate quote — or a project you commission a year later — you're buying two things at the price of one, and the audit trail starts a year late.
Usability. A 7-inch color touch screen — the V6.5's display — changes how a shift operator interacts with the instrument. Program selection by tap, results on screen, no cable to a side PC. Small thing. Big thing, on a line that runs 16 hours.
Operating envelope. The V6.5 runs at ambient +5 to +40 °C, 10–80% relative humidity, 8 kg on the bench. Check your actual room against your actual bench before the salesperson leaves the building.
From qualification to routine
The first run on a filter set defines the baseline everything else is judged against. The dry-bubble condition. The diffusive-flow reference. The pressure-hold slope. After that the routine repeats — same method, same cycle, same record format — so every later result is comparable to the first. That's the whole point of the historical-record function, and it's why the record count on the spec sheet matters more than the display size.
A machine that holds the program in memory and the history in its own storage is the machine that stays validated. The Integtest V6.5 and V8.0 are both specified with GAMP-aligned conditions, 21 CFR Part 11-compliant records and the IQ/OQ/PQ package included. The instrument that arrives is the instrument your validation file describes. That's the sentence you want the auditor to read.
Three buying mistakes we see again and again
Spec'ing one method. You order the bubble-point box because that's what the current procedure runs. Six months later the procedure adds diffusive flow post-use, and you're re-buying. The full set costs less than the gap.
Ignoring post-use. The 2022 revision made it a non-destructive post-use requirement, and a lot of older spec sheets don't mention it at all. Read your own procedure, not the vendor's sample spec.
Records that die on the instrument. If the data can't get to your LIMS in the shape your quality system reads, the test is only half done. Ask to see a real export, not a screenshot of the screen.
Standards and sources
This guide draws on the primary documents below. Read them with your procedure open — the gap between the two is usually where the program lives.
USP <43> — Filter Units · EU GMP Annex 1 — Sterile Medicinal Products (EMA) · FDA Guidance for Industry — Sterile Drug Products Produced by Aseptic Processing (2004)
Scoping a filter integrity program?
Tell us your procedure and your membrane — we'll come back with method coverage, configuration and documentation.
Talk to Our Team