Request test volume and review the Certificate of Analysis

Before running any cell-based assays, review the CoA from your supplier. Key parameters to check: total protein (typically 35–45 mg/mL for standard FBS), haemoglobin (<25 mg/dL for low-haemoglobin grade), endotoxin (<10 EU/mL standard; <5 EU/mL low endotoxin; <1 EU/mL ultra-low), pH (6.8–7.6), osmolality (260–340 mOsm/kg), mycoplasma negative, sterility pass.

Request a test volume of 100–500 mL — sufficient to run at least 3 independent validation experiments in parallel with your current reference lot.

Prepare both lots identically for testing

Thaw the test lot and your current reference lot under identical conditions (37 °C water bath, <30 min). Heat-inactivate both if your protocol requires it (56 °C, 30 min). Aliquot and store identically. Do not introduce any variable between the two lots other than the lot identity itself.

Run a proliferation / growth assay with your most sensitive cell line

Seed your most serum-sensitive cell line at a defined density in triplicate wells using both the reference lot and the test lot at your standard working concentration (typically 5–10%). Count cells (or measure absorbance via MTT/MTS) at 48 h and 96 h. Calculate growth rate and doubling time. Acceptance criterion: test lot growth rate within ±15–20% of the reference lot, or as defined by your internal specification.

Run your application-specific functional assay

Growth support alone is not sufficient — validate the lot in the assay context it will actually be used in. For mAb producers: measure antibody titre or cloning efficiency. For diagnostics development: run your target immunoassay and compare signal-to-noise with both lots. For viral vector work: compare transduction efficiency or titration results. This is the most critical step and the one most labs skip when under time pressure.

Run a sterility and mycoplasma check on the test volume

Even if the supplier provides a CoA with mycoplasma negative status, running a rapid PCR-based mycoplasma test on your received material adds an additional layer of assurance and creates a documented in-house record. For regulated manufacturing environments, this is a GMP requirement. For research labs, it is best practice that catches rare shipping or handling contamination events.

Document and make the lot acceptance decision

Record all results in a lot validation report: lot number, origin, supplier, receipt date, test volume, cell line used, assay methods, results vs. acceptance criteria, and final accept/reject decision. Archive the CoA, CoO, and any supplier-provided TSE/BSE or viral safety documentation alongside the report. This record is your reference if the lot is challenged in an audit or regulatory submission.

Reserve the bulk lot before ordering

Once the test volume passes your acceptance criteria, contact your supplier to reserve the remaining lot volume. In a shortage market, validated lots sell out quickly. Lot reservation locks in your tested specifications — you order the same lot you validated, not a substitute.