Freeze-Thaw and the Damage You Cannot See

Part of Clinical Laboratory (LAB) Training: Storage, Freezers and Excursions.

About 2 minutes. Free, in your language, no account needed.

Cycles count, and they are cumulative

Many analytes tolerate one freeze-thaw and not three. Protein structure changes, cells rupture, and concentrations shift.

The manual will often state a maximum number of cycles. That number is a limit on the sample's whole life, not on what happens in your laboratory.

A sample looks the same afterward

This is what makes it dangerous. There is no visible sign that a sample has been thawed and refrozen twice.

The only protection is the record. If cycles are not logged, nobody downstream can know.

Log every thaw

Even a partial one. Even when the sample was out for two minutes and went straight back.

A sample retrieved for a shipment that was then cancelled has been through a cycle. It counts.

Aliquoting exists partly to prevent this

The reason the manual asks for five small aliquots rather than one large one is so a later assay uses one aliquot and leaves four untouched.

Thawing the whole volume to take a portion defeats the design. If you need less than an aliquot, that is still one cycle on that aliquot and zero on the rest.

Thaw as the manual says

On ice, at room temperature, in a water bath at a stated temperature. These are not interchangeable.

Rapid thawing damages some samples. Slow thawing extends the time an unstable analyte spends in solution. The method is specified because it matters.

Never refreeze without checking

For some studies refreezing is prohibited outright. For others it is permitted within a cycle count.

If you are unsure, hold the sample at the thawed-state storage condition and ask. Refreezing first and asking afterward cannot be undone.

What to record

Date and time out, date and time returned, the reason, the thaw method, and the cumulative cycle count.

That last field is the one people omit, and it is the one the next person needs.