Traceability and what breaks it

Traceability is the ability to follow a material through every step of its life using the records it left behind. Backward traceability starts with a container on the shelf and works back to the supplier lot, the receiving record and the certificate that came with it. Forward traceability starts with a supplier lot and finds every place it went: which batches it was used in, which containers were filled from it, where those containers were sent. Both directions rely on the same thing, an identifier that stays with the material and appears in every record that touches it.

In practice that identifier is usually a lot or batch number, sometimes supplemented by a container number or an internal receiving code. When the chain works, a question about one container can be answered in minutes. When it breaks, the answer is often “we cannot tell,” and the only safe response is to treat every item that might be affected as affected.

Two meanings of the word

Laboratories use the word in a second sense as well. Metrological traceability, defined in the international vocabulary of metrology and required by ISO/IEC 17025, means that a measurement result can be related to a reference, usually an SI unit, through an unbroken chain of calibrations, each with a stated uncertainty. A balance is traceable in this sense when its calibration weights were calibrated against higher standards, which were calibrated against higher ones still. The two meanings share an idea: every link has to be documented, and one missing link breaks the whole chain. This piece is about the first meaning, the trail a material leaves.

Where the chain usually breaks

Breaks rarely happen in the database. They happen at the bench, at the loading dock and in the cold room, at moments when someone handles material and the paperwork does not keep up. The common points of failure are familiar to anyone who has run an investigation.

Subdividing without a new identity. A large container is split into smaller ones for convenience, and the smaller containers are labeled with the material name but not the lot number, or with a handwritten label that does not say which parent container they came from. Every subdivision is a new container and needs a label that links it to its parent, plus a record of when and by whom it was made.

Combining lots. Two partly used containers of the same material are poured together to free up space. The result now holds two lots and the label can only name one. Combining should be avoided; where it cannot be, the new container needs its own identity and a record of what went into it.

Relabeling and repacking. A label is replaced because it was damaged, or material is moved into a different container. If the new label is not checked against the old one and the change recorded, the link to the original supplier documentation is lost.

Receiving shortcuts. A delivery is put away before it is logged, or the receiving record notes the material but not the supplier lot number printed on the container. Every later record then refers to an internal code with nothing behind it.

Transcription. A lot number is copied by hand from a container to a notebook and a digit is changed. The record now points to a lot that may exist and may be the wrong one, which is harder to catch than a number that does not exist at all.

Keeping the chain intact

The controls are simple to describe and take discipline to keep. Record the supplier’s lot number at receipt, together with the date, quantity, condition on arrival and the certificate received. Give every container a label that carries the material name and its lot or container identifier, and give every subdivided container a label that also names its parent. Record each use of a material by lot number at the time of use, in the controlled record for the work it was used in. Where possible, scan barcodes instead of copying numbers by hand. Keep unidentified material out of use until its identity is established, and dispose of it under a procedure if it cannot be.

Shipping and receiving records deserve the same care as laboratory records. A container that arrives without a lot number on its label, or with a lot number that does not match the accompanying certificate, should be quarantined until the discrepancy is resolved with the sender. Accepting it and sorting out the paperwork later is how an untraceable container gets onto the shelf.

The test of a traceability system is a mock recall: pick a supplier lot and see how quickly every use of it can be listed, then pick a finished container and trace it back to its sources. Many quality systems run this exercise on a schedule, because a chain that has never been tested has usually broken somewhere without anyone noticing.