Pre-acceptance testing, often written PAT, is the check a laboratory makes on a new lot of reagent, calibrator or control before the lot is allowed into routine use. It exists because a new lot is a change: same product name, different manufacturing run, and sometimes a different result. ISO 15189:2022 clause 6.6.3 requires that each new lot or shipment is verified for performance before use, and the laboratory, not the supplier, carries that duty.
Why a new lot is treated as a change
Two boxes of the same reagent from two lots can differ in calibration, in reactivity, or in how they behave with a particular control. Most of the time the difference is invisible. Occasionally it is a shift large enough to move patient results across a decision limit. The purpose of pre-acceptance testing is to find that shift on the bench, with a handful of samples, before it reaches a report. The supplier's certificate of analysis says the lot met the manufacturer's specification; it does not say the lot performs acceptably on your analyser, with your calibrator, against your controls.
What the test usually involves
The standard sets the requirement, not the method, so laboratories design their own. A typical acceptance check for a reagent lot runs the new lot in parallel with the current lot on the same day, using quality control material at two or more levels and a small set of patient samples across the reportable range. The results are compared against acceptance criteria the laboratory has set in advance: a maximum bias between lots, or agreement within a defined allowable error. For a calibrator lot, the check is that assigned values recover within limits on the current reagent. For a control lot, the check establishes the target mean and range that will be used to judge every run from then on.
The outcome is a decision, recorded by name and date: accepted for use, or rejected and quarantined. A lot that has been tested but not yet signed off is neither; it stays out of use until the decision is made.
Who does it
The scientist responsible for the assay does the testing, and a senior scientist or the section supervisor signs the acceptance. In a single laboratory that is usually the same team that received the box. In a larger network the acceptance decision often lives in a central register, kept by the section that runs the testing, and every receiving bench across the network is expected to check the register before a lot goes onto a shelf as usable stock.
That arrangement works only if the person receiving stock can see the register's current state at the moment the delivery lands. If the register is on a shared drive that is checked later, or checked from memory, the lot has already been shelved next to accepted stock, which is the situation clause 6.6.4 exists to prevent.
What must be recorded
Three things, kept so that an assessor can follow them from the delivery to the bench.
- The status of the lot at receipt. Accepted already, testing in progress, awaiting sign-off, rejected, or never seen before. A lot that is new to the laboratory must be flagged as new the moment it arrives, because that flag is what starts the test.
- The test itself. The date, the operator, the material and samples used, the results, the criteria and the decision. Most laboratories keep this as a worksheet per lot.
- The changeover. The date the accepted lot first went into use, so that any result can be traced to the lot that produced it.
Where it goes wrong
The common failures are ordinary. A new lot is received on a busy afternoon and used the next morning because nobody noticed it was new. A lot is tested, passes, and the sign-off never happens, so the paperwork says it is not accepted while the bench has been using it for a fortnight. The register is updated, but the reagent log still says nothing about it. Each of these is a finding, and each of them is a record problem rather than a science problem.
How LotWarden handles it
LotWarden puts the register check at the door. When a delivery docket is read, every lot on it is looked up in the department's own pre-acceptance register and in the reagent and calibration logs back to January, and given a verdict on the spot: accepted, awaiting sign-off, testing in progress, rejected, or not on the register. First receipt of a lot is badged as a new lot. Every lot that is not yet accepted goes onto an investigation worklist, worst first, with the action required and blank columns for who investigated and the outcome. When the receipt is written into the log, the verdict travels with it as the comment, so the reagent log and the register say the same thing on the same day. The testing itself, and the decision, remain the laboratory's own process.