When the Kit Leaves the Building: A Practical Surveillance Rhythm for Antibody Diagnostics
Post-market surveillance (PMS) has a reputation problem in small diagnostics companies. It is often treated as the complaint inbox with a regulatory label attached: something to be checked when a customer emails, and reviewed in earnest only before an audit. For antibody-based in vitro diagnostics, that approach misses the point. The reagent is not static after launch. Antibody lots vary, conjugates age, membranes shift, buffers interact with sample matrices, and laboratories use kits in ways that no validation protocol fully anticipates. PMS is the evidence loop that asks whether the product continues to perform in routine use, and whether something in the system is changing.
As of 2026, UK developers of antibody diagnostics operate under UK MDR requirements and MHRA vigilance expectations, with UKCA marking in scope for many products. The regulatory language is important, but the operational question is simpler: how does a small team notice a problem early, decide what it means, and act without waiting for an annual review? The answer is a rhythm, not a binder.
PMS is not pre-market validation repeated
Pre-market validation answers a bounded question: does the assay perform as intended under defined conditions? PMS asks a different question: does it continue to perform as used, and what is changing? Validation evidence is generated before launch and is largely fixed. PMS evidence accumulates after launch and should be allowed to challenge assumptions. A kit that met its claims in a validation laboratory may still show lot-to-lot drift in a busy NHS laboratory, or a false-positive pattern in a sample type that was underrepresented in the original study.
The distinction matters because teams sometimes treat PMS as a lighter version of validation. It is not. Validation is a gate; PMS is a listening system. It should be designed to detect changes in reagent performance, user behaviour, storage conditions and sample populations, and to route those observations to the right decision.
Begin with a narrow, disciplined intake
A surveillance system is only as good as the information entering it. For antibody diagnostics, complaint intake should capture a small set of fields consistently: product and kit code, reagent lot, component lot where known, date of receipt, customer type, assay platform, sample type, failure mode, patient impact, and whether the issue was repeatable. One owner should receive and acknowledge complaints, and a two-working-day acknowledgement is a reasonable internal target for most small teams.
It is equally important to separate complaints from enquiries. A question about storage does not need a CAPA; a report of reduced signal with a specific lot does. Antibody-specific prompts help: was the conjugate lot recorded, was the kit reconstituted correctly, was the sample frozen and thawed, was there a change in wash buffer, and did the issue appear across multiple operators? These details turn a vague report into a reviewable event.
The monthly hour that replaces the annual scramble
A monthly review is more useful than an annual retrospective because trends are visible while they are still small. The meeting need not be long. One hour, a fixed agenda and a one-page record are enough for many small UK biotech teams.
A practical monthly template can be kept to one page:
| Review area | Question to ask | Record |
|---|---|---|
| Complaint volume | How many new complaints, and are they above the expected baseline? | Count and rate per 1,000 kits |
| Lot pattern | Are complaints clustered by reagent lot or component lot? | Lot numbers and rates |
| Failure mode | Is the same antibody-related failure recurring? | Signal loss, drift, cross-reactivity, interference |
| Severity | Is there a credible risk of false results affecting patient care? | Severity rating and rationale |
| Regulatory route | Does this require a vigilance assessment? | Decision and date |
| CAPA status | Are open actions linked to complaints and lots? | Action owner and due date |
| Effectiveness | Did the last action reduce the signal? | Before-and-after trend |
This is not a substitute for a formal PMS plan. It is the working record that makes the plan real.
Trend review: look for the lot behind the lot
Antibody diagnostics generate useful trend data because the critical reagents are traceable. Plot complaint rates per 1,000 kits by finished lot, then, where possible, by conjugate lot and capture antibody lot. A cluster that appears in one finished lot may originate in a component lot; a cluster across finished lots may point to a supplier change or a storage excursion. Review control data and repeat-test results alongside complaints, because a rise in complaints may reflect a change in customer mix rather than reagent performance.
Small teams should resist the temptation to explain every spike. Some variation is normal. The purpose of trend review is to identify sustained shifts or patterns that exceed the thresholds set in the PMS plan, not to produce a narrative for every data point.
Signal triage without a standing committee
Signal triage should be documented, proportionate and quick. A simple matrix combining severity, frequency and detectability is sufficient for many antibody IVDs. The output should be one of four decisions: observe, investigate, open a CAPA, or conduct a vigilance assessment. Record the rationale, even when the decision is to take no further action. This protects the team during audit and helps future reviewers understand why a signal was not escalated.
A single complaint is rarely a signal on its own. A single complaint involving a false negative in a clinical setting is a different matter. The triage matrix should make that distinction explicit rather than relying on memory.
CAPA linkage and field safety notices
Not every complaint requires a CAPA, but every CAPA decision should be traceable to the complaint or trend that prompted it. Where an investigation identifies a root cause, link the action to the affected lot, supplier or process. Where no root cause is found, record the justification and the monitoring plan. Effectiveness checks should look at subsequent lots, not only at whether the action was completed.
If the evidence suggests a risk to patients or users, the team should assess reportability to the MHRA under UK vigilance requirements. Field safety notices should be clear, UK-specific and proportionate. It is not necessary to wait for a perfect root cause before taking action; it is necessary to document the risk assessment and the decision.
A rhythm, not a ritual
The purpose of PMS is not to satisfy an auditor. It is to shorten the distance between a change in the field and a decision in the company. For antibody diagnostics, where lot-level variation and reagent stability are central to performance, a monthly surveillance rhythm gives small UK teams a realistic way to see the signal after launch. The kit leaves the building, but the evidence does not stop there.
