Part I showed that controlling the biological component is fundamental to achieving consistent potency results.

But standardisation is only the starting point: the assay must still demonstrate that it delivers accurate, precise and reliable measurements suitable for regulatory use.
Adopting a cryopreserved cell system addresses the sources of variability described above, but the regulatory requirement for a validated assay remains.
ICH Q2(R2), the primary guidance on analytical procedure validation, defines core performance characteristics that a cell-based potency assay must demonstrate before it can be used in a GMP lot release context.
Accuracy describes how closely the assay measures the true potency of a sample.
In a relative potency assay, it is assessed by preparing samples at known levels spanning the working range (50–200% of the reference standard) and determining how closely the measured values recover the theoretical input.
Recovery values should fall consistently within 85–115% across this range.