From swab to sequencer: the journey a sample survives
A specimen for hereditary-cancer testing can travel a thousand miles between the cheek it came from and the flow cell that reads it. This hub gathers what the evidence says about packaging, preservation chemistry, and the cold chain — so the DNA that arrives is the DNA that left.
The pre-analytical phase decides the result
Long before a variant such as BRCA1 c.68_69del is called in a report, the molecule carrying it has to reach the laboratory intact. Most errors in genetic testing are not sequencing errors — they are pre-analytical: the window between a sample leaving the body and the assay beginning.
Three variables dominate that window. Packaging determines whether the specimen arrives at all, and whether it does so legally — clinical samples ship as UN3373 "Biological Substance, Category B" under triple-packaging rules. Preservation chemistry decides whether nucleic acids degrade in transit; a lysis-and-stabilisation buffer can hold genomic DNA at room temperature for months. Temperature matters most for the analytes the buffers cannot fully protect — RNA, plasma cell-free DNA, viable cells — which is where the cold chain earns its name.
The spokes below take each of these in turn.
The three pillars of specimen transport
Each spoke is an evidence-led explainer. Together they cover the full chain of custody from collection device to laboratory accessioning.
Biohazard shipping containers
Triple packaging, the UN3373 diamond, absorbent liners, and the P650 drop test — what makes a Category B parcel compliant rather than just a box.
Preservation buffers
How stabilisation reagents in devices like OG-500 and RNA-protectant tubes hold nucleic acids intact at ambient temperature, and where their limits lie.
Cold-chain handling
The four working temperature bands — ambient, 2–8 °C, frozen, and cryogenic — plus dry-ice and liquid-nitrogen logistics for fragile analytes.
ReadSample stability by method and storage condition
Stability depends almost entirely on the analyte (DNA is robust; RNA and viable cells are not) and on whether a stabilising buffer is present. The figures below are drawn from manufacturer technical data and peer-reviewed pre-analytical studies; treat them as published ranges, not guarantees for a specific protocol.
| Specimen / device | Typical volume | Stable at room temp | Cold-chain need | Primary analyte |
|---|---|---|---|---|
Stabilised saliva (OG-500) | ~2 mL | Months to years (mfr. claims up to 5 yr) | None for transport | Genomic DNA |
| Buccal swab (dry) | 1–2 swabs | Days to weeks | Keep dry; cool if delayed | Genomic DNA |
Whole blood, EDTA (K2EDTA) | 3–10 mL | ≤ ~3 days for gDNA | 2–8 °C if delivery > a few days | Genomic DNA |
| Plasma for cell-free DNA | varies | Hours unless stabilised | Freeze at −80 °C for storage | cfDNA |
Whole blood for RNA (PAXgene) | 2.5 mL | Per tube spec (stabilised) | Freeze per protocol; RNA degrades fast unstabilised | RNA |
| FFPE tissue block | n/a | Stable (cross-linked) | Ambient; protect from heat | Fragmented DNA/RNA |
Table 1. Indicative stability of common hereditary-cancer specimen types. Always defer to the receiving laboratory's accessioning criteria.
Cold-chain working temperatures, illustrated
Four bands cover almost all specimen transport. The chart shows the upper temperature of each band (less-negative = warmer); cryogenic shipping sits far below the others. Values are nominal industry reference points.
Stabilised saliva, FFPE — buffer or matrix does the work
EDTA whole blood, many clinical specimens
Plasma, cfDNA, biologics; sublimes over ~1–2 days
Viable cells; dry shippers hold up to ~10 days
Logistics glossary
A few terms that recur across the spokes.
- UN3373
- United Nations classification for "Biological Substance, Category B" — patient diagnostic specimens that are not in the highest-risk Category A. Shipped under Packing Instruction P650.
- P650
- The IATA/ICAO packing instruction for Category B: leak-proof primary receptacle, absorbent material, a sealed secondary receptacle, and a rigid outer surviving a 1.2 m drop, with the diamond mark ≥ 100 × 100 mm.
- Triple packaging
- Primary (the tube), secondary (sealed, leak-proof, with absorbent), and outer (rigid, labelled) — the layered system that keeps a specimen contained even if the primary fails.
- Dry shipper
- A vacuum-insulated vessel charged with liquid nitrogen absorbed into a porous lining, holding ~−150 to −196 °C for up to ~10 days with no free liquid to spill — the way viable cells travel.
- [1]IATA / ICAO. Packing Instruction P650 — Biological Substance, Category B (UN3373): triple-packaging, absorbent, 1.2 m drop test, and marking requirements.↗
- [2]DNA Genotek. Oragene technical data: expected DNA yield and long-term ambient stability of stabilised saliva (OG-500 series).↗
- [3]PLOS ONE 2017. Storage temperature and duration effects on DNA and RNA quality from whole blood samples.↗
- [4]NCI / DCTD. Biospecimen Evidence-Based Practices: cell-free DNA collection, processing, and storage (freeze plasma at −80 °C).↗
Built for understanding, not instruction
These explainers describe how biospecimen logistics works in research and clinical settings. They are not protocols, and nothing here is medical advice — if you are weighing a hereditary-cancer test, speak with a clinician or genetic counsellor. To go deeper into the science, start with our guides.