Most of the reagent failures we hear about aren't manufacturing failures but storage failures: a vial thawed and refrozen, a bottle kept at −20 °C that needed −70 °C, an aliquot left on the bench through a long lunch. Biological reagents are proteins in water, and proteins in water are fussy about temperature. This is how to keep a product the way the lot certificate describes it.
The label temperature is the specification
Storage conditions on a label aren't conservative defaults. They're the conditions under which the shelf life was established. Stability guidance for drug products, which the biologics industry follows for its own reagents, requires that a shelf life be supported by real-time data at the labeled long-term storage condition (FDA / ICH Q1A(R2)). Store a product warmer than its label and the expiry date stops meaning anything.
The conditions you'll see on our labels:
- −70 °C or colder for complement and for coagulation plasma, where the labile components (complement proteins, factors V and VIII) decline measurably at −20 °C over months.
- −20 °C or colder for most sera, plasmas and whole-blood-derived products.
- 2 to 8 °C for lyophilized powders (complement, albumin, gamma globulin) before reconstitution, and for fresh whole blood, red cells and fresh tissue, which must never be frozen.
- Room temperature, dry, isn't a storage condition for anything we sell, apart from briefly for a lyophilized vial in transit.
Freeze-thaw
Each freeze-thaw cycle stresses proteins twice. Ice formation concentrates solutes and shifts pH in the remaining liquid, then thawing exposes the proteins to aggregation as they rehydrate. Complement loses hemolytic activity with every cycle, enzymes lose activity, antibodies aggregate and precipitate. And the vial looks exactly the same afterwards.
The fix is to thaw once. On first use, thaw the vial completely, mix gently, and split it into single-use aliquots in tubes that seal well at low temperature. Label each one with the lot number and date. For complement, thaw rapidly in a 37 °C water bath just until the last ice disappears, put it on ice, use it within the working day, and discard what's left rather than refreezing it. Serum and plasma tolerate a slower thaw at 4 °C overnight. If cryoprecipitate forms, warm it to 37 °C to redissolve it before you aliquot.
Lyophilized products
Freeze-dried reagents avoid the freeze-thaw problem entirely until they're reconstituted, which is why lyophilized complement and immunoglobulins are the practical format for shipping to sites without ultra-low freezers and for kits. Store the sealed vial refrigerated, let it reach room temperature before opening so moisture doesn't condense on the powder, reconstitute with the specified diluent, and then treat the solution like any liquid product: aliquot, freeze, thaw once.
The expiry date
The expiry assumes the labeled condition from the day of manufacture. Three things shorten it in practice. Time in transit, which is why we ship on dry ice and ask you to freeze on arrival. Excursions in your freezer (check it, and know what a defrost cycle does to the top shelf). Opening counts too: an opened liquid vial or a reconstituted powder is a new product with a shelf life measured in days to weeks, not the date on the label.
The habits that prevent most of this are simple. Freeze reagents the day they arrive, at the label temperature, and note the arrival condition. Aliquot on first thaw and never refreeze a partially used vial. Keep a freezer log and an alarm; a −80 °C freezer that drifts to −50 °C over a weekend has changed your reagents. Use the oldest lot first and record the lot number with every experiment. And when a result drifts, check the storage history before you suspect the assay.
If you're not sure whether a lot that saw an excursion is still usable, ask us with the lot number and what happened. For complement we can advise on re-titering before you decide.