In February, a courier box sits on a loading dock in Winnipeg for forty minutes while the driver finishes a delivery. The samples inside were cool when they were packed and are frozen when they arrive. In July, the same box crosses a parking lot in a heat wave and arrives warm. Nothing was spilled, nothing was mislabelled, and both shipments are rejected anyway.
Cold chain is the part of specimen transport that has nothing to do with the sample and everything to do with the box around it. Canadian conditions make it a seasonal problem: the same packaging that protects a sample in a mild week fails at minus thirty.
What Cold Chain Means for a Diagnostic Sample
A cold chain is a documented sequence of storage and transport conditions that keeps a sample within the temperature range its assay assumes. The range is set by the test, not by the packaging: a culture may do better cool, a coagulation sample may need to stay at room temperature, and a frozen assay leaves the site at minus twenty or colder. Packing a whole shipment to one temperature is therefore a common mistake, particularly when samples destined for different assays travel in the same box.
Temperature Ranges by Sample Type
| Sample group | Typical transport condition | Common failure |
|---|---|---|
| Routine urine, dipstick or chemistry | Refrigerated, protected from freezing | Left at room temperature; frozen in transit |
| Urine culture | Refrigerated after collection, processed promptly | Delay before refrigeration; overgrowth |
| Whole blood in EDTA for cell counts | Room temperature, analysed within the assay window | Refrigerated, causing cold agglutination artefacts |
| Coagulation samples | Room temperature, tested within the assay window | Chilled in transit; under-filled tube |
| Ammonia, lactate and similar analytes | Chilled or on ice, delivered fast | Time out of range rather than temperature alone |
| Samples for frozen assays | Frozen solid from the moment of separation | Partial thaw and refreeze |
The table is a starting point, not a substitute for the receiving laboratory's instructions. The instruction that governs is the one attached to the test you are sending, and it should be the version your collectors are reading this month.
Gel Packs, Ice Packs and Dry Ice
Conditioning refrigerated packs
A gel pack pulled from a freezer is not a refrigerated pack; it is a frozen block that will chill whatever it touches. Condition packs before use so they hold the target range rather than pulling the sample below it: either let them reach the intended temperature, or freeze them and allow them to temper for the interval your procedure specifies. Packs should be wrapped or separated so they are not in direct contact with the primary container, because direct contact creates local freezing even inside a box that averages the right temperature.
Dry ice and the frozen chain
Dry ice holds a very cold range and vents carbon dioxide, which means the outer packaging has to allow gas to escape and the shipment has to comply with the dangerous goods rules for the quantity you are sending. For small volumes, insulated boxes with the correct quantity of dry ice are usually adequate for a day's transit; for multi-day routes, the route itself becomes part of the design. Frozen shipments also need a clear instruction that partial thawing is not repairable: a sample that has thawed and refrozen cannot be sent on.
Winter and summer failure modes
Canadian conditions create two opposite problems. In winter, an unconditioned shipment can freeze a sample that should have stayed refrigerated, and the damage is invisible in the packing slip. In summer, a box left in a vehicle raises the internal temperature well above ambient, and a sample that should have stayed cool drifts out of range within an hour. Both are route problems as much as packing problems: a courier with a temperature-controlled vehicle or a shorter handover window removes failures that no amount of ice can fix.
Documenting an Excursion
Record the temperature at packing, the temperature at receipt, the time out of range, and the action taken. Six fields cover almost every requirement: sample identifier, test, packing time and temperature, receipt time and temperature, duration of any excursion, evaluation of whether the assay is affected, and the decision to accept or reject.
Where samples are routine and the route is short, a daily log of packing temperatures combined with an exception note may be enough. Where the assay is sensitive or the route is long, a temperature indicator in the box is the practical answer: it produces a record regardless of who handles the shipment, and it turns a dispute with a courier into a documented fact.
Packaging That Supports the Cold Chain
Cushioning, containment, absorbent material, and a rigid outer container form the base layer, and the secondary container has to meet the pressure and integrity requirements of the transport regulations that apply to your shipment. A 95 kPa specimen transport bag with a separate document pocket is the usual secondary container; it keeps paperwork dry and identifiable while the absorbent and rigid layers do the protection work.
Two habits matter as much as the packaging list. Keep pre-conditioned packs where the packing bench is, so conditioning happens without a trip to a freezer. And write the packing sequence down, including how many packs go into which box size, so the routine does not change with the person doing the packing. Collectors who also handle a graduated leak-proof specimen cup will want the primary container sized to the bag, and sites running sterilizers can request a biological indicator trial pack.
Related Reading
- Specimen shipping and packaging compliance rules
- Laboratory biohazard waste handling
- Earlier in this series: pediatric specimen collection
- Next in this series: setting up a sample collection site
- Browse clinic supplies for collection-room consumables
Frequently Asked Questions
How long can a specimen stay out of the fridge before it is unusable?
That depends entirely on the test, and the stability window is stated in the receiving laboratory's collection instructions. Some analytes are stable for hours at room temperature while others begin to change within minutes. When the instructions are unclear, call the laboratory before sending the sample rather than after it has been rejected.
Do gel packs need to be conditioned before packing?
Yes, if the target range is refrigerated rather than frozen. A pack straight from the freezer can take a sample below its required range, which damages some tests as effectively as heat. Condition packs to the target temperature, and keep them off direct contact with the primary container.
Can frozen samples be re-frozen after a partial thaw?
Generally no. Once a frozen sample begins to thaw, the assay it was destined for may no longer be valid, and the release of cellular contents during freeze-thaw cycles changes many analytes. The safe course is to treat a thaw as an excursion, document it, and let the laboratory decide whether the assay is still possible.
What should a temperature excursion record contain?
The sample identifier and test, the packing date and time with the temperature at packing, the receipt time and temperature, the duration out of range, an evaluation of the likely effect, and the decision taken. That combination lets a reviewer reconstruct the event and lets the laboratory justify accepting or rejecting the sample.
Is a temperature indicator required in every shipment?
Not always. Requirements come from your own quality system, the receiving laboratory's instructions, and the transport regulations that apply to your route. Many sites use indicators on sensitive assays and long routes and rely on documented packing temperatures plus exception reporting for routine local deliveries.
Last updated: September 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334, Importer, Class I).
Related Reading
Explore more guides in this category:
0 comments