Follow the lot, not just the label.

The medium is an experimental condition

Cantor and colleagues developed human plasma-like medium and showed that its composition altered cellular metabolism relative to traditional media. In their experiments, uric acid inhibited UMP synthase and reduced cancer-cell sensitivity to 5-fluorouracil. This was evidence about formulation and biological context, not a demonstration that every difference between two commercial lots changes an assay. ^[1]

A separate study by Liu and colleagues compared eight commercial FBS products and found differences in baseline IL-8 expression in epithelial cells; the same pattern was not seen for TNFα and IL-1β. The study supports attention to the material used for a particular readout. It does not establish a universal ranking of serum products or isolate lot-to-lot variability within a single product. ^[2]

Together, these findings make a practical point: a medium name alone is too coarse for some scientific questions. The guidance below is about preserving the information needed to investigate a difference. Selecting or changing culture conditions still requires assessment for the model and endpoint in question.

Distinguish formulation, supplier lot and prepared lot

The formulation describes what you intend to make. The supplier lot identifies a manufactured material. The prepared lot identifies a particular preparation in your laboratory. An aliquot or working container may then need its own identifier if its storage or handling history can diverge. Use these terms consistently so that “batch” does not mean a reagent shipment in one record and a culture in another.

Create a preparation record that points to the formulation version and the source materials actually used. Supplier name and catalogue number distinguish products; lot numbers distinguish deliveries of the same product. Record units alongside quantities and do not treat an empty value as zero.

GIVIMP’s second edition treats apparatus, materials and reagents, method performance, reporting, and record retention as connected areas of in vitro practice. Its regulatory focus is chemical safety assessment. For routine research, the field set below is a practical starting point to adapt to the material and the laboratory’s own procedures. ^[3]

• Prepared-lot identifier and formulation or protocol version.
• Preparation date, preparer and the quantity prepared, with units.
• Source-material names, supplier/catalogue identifiers and actual lot numbers.
• Assigned expiry and storage conditions, with their basis in the relevant procedure or supplier information.
• Applicable checks, release decision or restrictions, and the location of supporting records.
• Container or aliquot identifiers where separate handling histories matter.

Record the lot at the point of use

A preparation record is only half the chain. Link the actual lot to the dated culture action in which it was used. A lot selected during planning is an intention; a lot recorded after checking the bottle at the bench is evidence about use. If the plan changes, record the material that was actually used and explain a relevant deviation.

Make the bottle label and the digital record resolve to the same identifier. Short, readable codes are useful, but they should be unique within the workspace and remain attached to their historical preparation. Avoid labels such as “new medium” or “Sarah’s bottle” as the only means of identification.

Keep volume prepared, volume dispensed and volume administered conceptually separate. They may differ because of overage, retained material, transfers or waste. Where volumes are recorded, preserve which quantity each field represents. An apparently balanced inventory should not be used to infer a missing culture-use record.

Plan a change of material before the old supply disappears

A new supplier lot, formulation revision, supplement source or preparation process creates a question: what evidence is needed to show that it is suitable for this use? Decide that before the change is absorbed into routine work. The comparison should reflect the outcome that matters to the model, rather than relying only on whether the cells remain alive.

The Geraghty cell-line guidelines advise retaining some of the previous medium-component batch when introducing a new one so that a comparison remains possible if problems emerge. They also note that a medium problem may become apparent only after several cell generations. Those points explain why the date of the material change belongs in the culture history. ^[4]

Agree the assessment criteria with the responsible scientist, preserve the comparison record, and make any restriction visible to the users of the new lot. There is no universal acceptable change in growth, morphology or assay response that applies to every culture. Avoid presenting a convenient local threshold as a general biological standard.

Investigate a suspected lot effect without assuming the answer

Start with a dated observation: which cultures or assay results changed, and when? Follow those cultures back to their material records, then follow the suspect lot forward to the other cultures that used it. Include preparations made from the same source component where relevant. This gives you a defensible set of records to review rather than a recollection of which bottles were nearby.

Compare the material history with other changes: passage history, operator, equipment, culture conditions, assay day or analysis method. If every treated sample used one lot and every control used another, the two explanations are confounded. A traceability link can reveal that design problem; it cannot statistically or biologically remove it.

Preserve the original observations, record why a lot is under review, and apply the laboratory’s process for deciding whether it remains suitable for use. Do not rewrite the historic formulation to match the replacement material. Document the investigation and the basis of the eventual decision, including uncertainty if causation was not established.

Test the record with a small traceability exercise

Select a recent culture action and ask a colleague to find the actual prepared lot, the formulation used, and the source-material identifiers. Then choose a prepared lot and ask which recorded culture actions used it. The two directions test different links; success in one does not guarantee success in the other.

Record where the exercise stalls. Missing source lots suggest a preparation problem; an unlabelled bottle suggests a point-of-use problem; culture actions linked only to a medium name suggest a recording problem. Fix the missing relationship rather than adding another spreadsheet that duplicates the same ambiguity.

Start with materials most likely to matter to your model or interpretation, then extend the approach where the risk justifies it. The useful outcome is not an exhaustive catalogue for its own sake. It is the ability to answer a specific scientific question about what the cells experienced.