Reagent Stability

Reagent stability is the evidence behind three numbers on a diagnostic kit: the shelf-life expiry date, the in-use (open-vial or on-board) period, and the storage and shipping conditions. Each is a separate claim and each needs its own study design. Real-time studies at the labelled storage temperature support the expiry date; accelerated studies at higher stress can support a provisional date while real-time data accumulates, but they do not replace it.

In-use stability covers what happens after the user opens a vial, reconstitutes a lyophilised reagent or loads it onto an instrument. Transport stability covers excursions in shipping, such as a cold-chain kit spending hours above its storage range. Stability is assessed against the reagent's performance specification, for example control recovery or signal within limits, not simply appearance.

In production, stability turns into operating rules: which lots go on study and at what pull points, how expiry is calculated for a kit whose components have different dates, what storage condition each lot is held at, and what happens when a pull fails. A failed pull may affect every lot made under the same formulation and may require customer notification, so the study must be traceable to the exact lots and formulation revision tested.

Guidance used by IVD manufacturers includes ISO 23640:2011 on evaluating the stability of IVD reagents (adopted in Europe as EN ISO 23640) and CLSI EP25. Labelled storage instructions and expiry are required on US IVD labels under 21 CFR 809.10. Paraphrased here; consult the standards themselves for requirements.

Related concepts: stability programme, reagent lot traceability, cold chain and stability-indicating method. Sources: ISO 23640:2011, CLSI EP25, 21 CFR 809.10.