Legionella test kits: instant rapid test vs UKAS lab sample kit - which do you need?

Use a rapid on-site kit when you need a same-day screen and can act on an indication; use a UKAS laboratory sample kit when the result must stand as evidence. No rapid kit is UKAS-accredited, every rapid-kit vendor states it must not replace laboratory analysis, and the cheapest kits detect serogroup 1 only.

That is the whole decision in one paragraph, but the two kit types get confused constantly, because they sit side by side in search results at similar prices and both call themselves a “legionella test kit”. They are different instruments answering different questions, and buying the wrong one either wastes money or, worse, files a screening result as if it were evidence.

The two kinds of kit

Type A: rapid on-site tests. A lateral-flow cassette, the same format as a covid test. You take the water sample, prepare it with the kit's buffer and filtration steps, and read lines on the cassette in about 25 to 35 minutes. No laboratory is involved. Every rapid kit on the UK market detects Legionella pneumophila antigen, with a detection limit around 100 CFU/L. Most of the market, whatever the box says, traces back to one manufacturer's lateral-flow technology - the DTK Water kit below is marketed as Hydrosense-derived, and the Accepta kit's specification sheet is near-identical.

Type B: laboratory sample kits. A bottle, a box and a returns label. You take the sample yourself following the instructions, post or courier it to a laboratory, and the laboratory cultures it under BS EN ISO 11731 - the reference method that grows and counts the organism over around ten days - then issues a report stating species, serogroup and count in CFU/L. The kit is just packaging; the product is the laboratory analysis behind it.

Two products get swept into this category by name only, and neither tests for legionella. Dip slides measure total general bacteria, not legionella - see dip slides vs lab testing for why a clean slide says nothing about legionella either way. And “legionella thermometer kits” (Kewtech, ETI and similar) are temperature-measurement kits: genuinely useful for the temperature monitoring that is the primary control on most systems, but they measure water temperature, not bacteria.

Which type do you actually need?

Work from the job, not the product page:

• “I'm out of temperature range and want a quick read before I escalate.” A rapid kit earns its keep here. An engineer standing next to a cooling tower or a caretaker with a failed calorifier gets a same-day indication to triage the situation - while the laboratory sample goes off in parallel if the indication is positive or the situation is serious.
• “I need to verify a treatment worked” (post-remediation, after a positive result, after a shutdown). Laboratory culture, every time. Verification is only worth having if the result stands as evidence, and a screening cassette is not evidence.
• “My written scheme or HSG274 sampling plan says I take samples.” Laboratory culture. A monitoring point in a control scheme exists to produce an accredited result you can trend and show an inspector.
• “I'm a landlord and just want to check a flat between tenancies.” Ask first whether you need to test at all. There is no legal requirement for landlords to test routinely, and for most simple domestic systems the risk assessment points to temperature control, not sampling. If you do sample, a postal laboratory kit is the type whose report means something in your records.
• “I need a number I can put in front of someone else” - an insurer, an auditor, an enforcing authority. Only an accredited laboratory report does this.

The serogroup caveat most listings bury

Legionella pneumophila comes in numbered serogroups. Serogroup 1 causes the majority of cases, but not all of them. The cheapest rapid kits - the LegionellaFast, Accepta and DTK products in the table - detect serogroup 1 only. The “Pro” and “Ultra” versions, at roughly £66 to £76 per test, extend that to serogroups 1-15. A negative on an SG1-only kit does not exclude serogroups 2-15, and no rapid kit detects the other legionella species (L. anisa, L. micdadei and the rest) at all. Laboratory culture under ISO 11731 identifies species and serogroups across the range, which is one more reason the laboratory remains the reference.

No rapid kit is UKAS-accredited - the vendors say so

UKAS accreditation applies to laboratories and their methods. A lateral-flow cassette you read by eye on a plant room floor is not an accredited method, and no rapid kit on the UK market claims to be one. The vendors are more honest about this than the search results suggest:

• Legionella Control International states of its rapid kit that it “should not replace routine laboratory analysis”.
• Accepta flags on its rapid kit product page that systems treated with biguanide or THPS biocides can produce false positives - a reminder that the cassette is a screening tool with known interferences, not a verdict.

Treat a rapid result accordingly: a positive is a reason to act and to confirm by culture; a negative is an indication within the kit's limits, not proof of absence.

The kits compared

Every product below is real and currently marketed to UK buyers. Prices are as found on 2026-08-02 and are snapshots, not quotations - confirm on the vendor's own page before buying. “Not published” means the vendor shows no price and quotes per enquiry. Inclusion is not endorsement, and no vendor has paid to appear.

* Dip-slides.com blocks direct fetching; those two prices were visible only in search-result snippets on 2026-08-02 and should be confirmed on the site before reliance. † uRisk's price comes from a page snapshot dating to late 2024; re-verify before quoting. Where a lab-sample vendor says “UKAS-accredited laboratory” without naming it, we record the lab as not published rather than guessing.

If you go the laboratory route, choose the lab, not the box

With a postal kit the bottle and branding are irrelevant; what you are buying is the laboratory analysis behind it. Two of the vendors above name no laboratory at all on their kit pages. Before buying any lab-sample kit, ask which laboratory will analyse your sample, get its UKAS accreditation number, and check the number's schedule covers legionella in water - the five-minute check set out on our testing laboratory directory, which compares verified UKAS-accredited laboratories on scope, method, turnaround and published price, several of which supply postal kits direct.

Whichever route you take, sampling follows BS 7592 and the result is only as good as the sample: how to take a water sample covers the method, and sampling and action levels explains what the counts mean when the report comes back. For the wider question of when sampling is and is not needed, see legionella testing - for most well-controlled systems, temperature control is the primary control and routine sampling is not required.