Sample stability & storage
How long the DNA in a swab, a saliva tube, or an EDTA blood draw stays trustworthy — by method, by temperature, and by how far it has to travel. A research-desk explainer for anyone trying to understand why a kit insists on room temperature and a clinic insists on ice.
Why stability is a method-by-temperature question
There is no single shelf life for "a DNA sample." Stability is set by three things at once: the collection chemistry (is the cell lysed and the nuclease inhibited, or is it just sitting in residual moisture?), the storage temperature, and the time-in-transit before a lab can process it.
Stabilising kits such as OG-500 saliva tubes lyse cells on contact and chelate the metal ions that endonucleases need, which is why they tolerate weeks of post and years on a shelf. An unpreserved liquid — fresh whole blood in EDTA, or a wet buccal swab — has no such protection, so it is racing the clock from the moment of collection. This page is an educational explainer, not medical advice; for a personal testing decision, speak with a clinician or genetic counsellor.
Stability by method × temperature
Representative, published stability windows for the common hereditary-cancer specimen types. Figures are typical ranges from manufacturer technical specifications and peer-reviewed storage studies; real-world windows depend on the exact kit, buffer, and handling.
| Method / sample | Typical volume | Room temp (15–30 °C) | Refrigerated (4 °C) | Frozen (−20 / −80 °C) | Notes |
|---|---|---|---|---|---|
Stabilised saliva (OG-500) | ~2 mL liquid | Up to ~5 years | Years | Longer (years) | Lyse-on-contact buffer inactivates nucleases; mailable by standard post |
| Buccal swab — dried | Single swab | ~1–2 weeks (declines fast) | ~14 days | Months+ | Untreated swabs lose reliable yield beyond ~1 week at room temp |
| Buccal swab — in preservation buffer | Swab + buffer | Up to ~1 year | Year+ | Year+ | Stabilising solution extends room-temp life dramatically |
FTA card (dried spot) | Card matrix | Long-term (archival) | Long-term | Long-term | Card binds DNA + denatures nucleases; designed for ambient archiving |
Whole blood, EDTA (unstabilised) | 3–10 mL | Extract within ~3 days | Up to ~10–14 days | Long-term | Apoptotic laddering appears by ~2 weeks at room temp |
| Whole blood in DNA stabiliser | Tube + reagent | Weeks | Weeks–months | Long-term | Yield/quality comparable to freezer-stored blood |
Purified genomic DNA in TE buffer | Eluate | Hours–days only | Short-term | Years (long-term) | Aliquot to avoid repeated freeze–thaw; EDTA chelates Mg²⁺ to block DNase |
Table 1. Approximate DNA stability window by collection method and storage temperature. Always defer to the kit insert and the receiving laboratory's own requirements.
Room-temperature stability at a glance
Order-of-magnitude comparison of how long each specimen type can sit at room temperature before DNA integrity is at risk. Shown on a log-style relative scale (approximate days) to fit short and long windows on one axis.
~1 week, then unreliable
extract within ~3 days
~2 weeks at 4 °C
~1 year
~5 years
Reading the degradation signs
What a lab actually looks for when deciding whether a sample is still usable. None of these require special equipment to understand, even if measuring them does.
- 01
Falling yield
Less total DNA recovered than expected for the input volume — the earliest, quietest sign, common in blood held too long before extraction.
- 02
Fragmentation / laddering
High-molecular-weight DNA breaks into shorter pieces; on a gel this shows as a smear or a regular 'ladder' from endonuclease cleavage, seen in room-temp blood by ~2 weeks.
- 03
Off A260/A280 ratio
A purity reading that drifts from the expected ~1.8 hints at protein or contaminant carry-over alongside degradation.
- 04
Amplification failure
The practical end-point: PCR or library prep that won't amplify, or amplifies only short targets — the sample can no longer answer the question asked of it.
The shipping window is part of the stability budget
Every day a sample spends in the post is a day spent against its stability window — which is exactly why stabilised saliva and dried-card formats dominate mail-in testing: they tolerate ambient temperature swings that would wreck a liquid blood draw.
For specimens that must move cold or that are regulated, diagnostic shipments typically travel as UN3373, Biological Substance, Category B under IATA Packing Instruction 650 — a triple-packaging system of a leak-proof primary receptacle, absorbent material, watertight secondary packaging, and a rigid outer box that has passed a 1.2 m drop test, with a solid-specimen limit of ≤4 kg per outer package.
Glossary
A few terms that recur whenever stability is discussed.
- Nuclease
- An enzyme that cuts nucleic acids.
DNaseactivity is the main driver of DNA degradation; stabilising buffers work largely by inhibiting it (often by chelating the Mg²⁺ it needs). - Freeze–thaw cycle
- Each round of freezing and thawing shears DNA. Aliquoting purified DNA before freezing avoids re-thawing a single stock repeatedly.
- UN3373 / Category B
- The transport classification for most diagnostic and clinical specimens, shipped under
IATAPacking Instruction 650 with a defined triple-packaging system. - TE buffer
- Tris–
EDTAsolution used to resuspend and protect purified DNA; theEDTAchelates metal ions to suppress nuclease activity during storage.
Common questions
Does freezing always preserve a sample best?
For purified DNA and long-term archiving, frozen storage at −20 °C or −80 °C is the conventional gold standard. But for many at-home collection formats, a stabilising buffer at room temperature is both adequate and more robust to shipping than freezing-and-thawing in transit. The right answer depends on the specimen type — see Table 1.
Why can stabilised saliva sit for years but a blood tube can't?
The saliva kit chemistry lyses cells and inactivates nucleases at the moment of collection. Unstabilised whole blood keeps live enzymes that begin fragmenting DNA almost immediately, which is why labs aim to extract within about three days at room temperature.
Is a sample 'ruined' the moment it passes its window?
Not necessarily — these are risk thresholds, not hard cliffs. Past the window, yield and integrity fall and the chance of an inconclusive result rises. A receiving laboratory decides acceptability against its own validated criteria.
How should I actually store or ship a kit I've collected?
Follow the specific kit insert and the laboratory's instructions exactly — they are validated for that product. This page explains the science behind those instructions; it does not replace them, and it is not medical advice.
- [1]DNA Genotek — Oragene. DNA Genotek. Oragene·DNA (OG-500) product specifications: DNA stable up to ~5 years at room temperature; longer at −20/−80 °C.↗
- [2]J Mol Diagn / Clin Biochem 2015. Quantitative analysis of genomic DNA degradation in whole blood under various storage conditions for molecular diagnostic testing — degradation apparent by ~2 weeks at room temperature; extract within ~3 days.↗
- [3]BioTechniques 2015. A method for preserving buccal swab samples for gDNA integrity — untreated swab room-temp stability ~1 week; preservation buffer extends to ~1 year.↗
- [4]QIAGEN — FTA technology. Indicating FTA cards: chemical matrix lyses cells, denatures nucleases, and binds DNA for long-term room-temperature archiving.↗
- [5]IATA PI 650 / DHL guide. Shipping UN3373 Biological Substance, Category B — triple packaging, 1.2 m drop test, ≤4 kg solid-specimen limit.↗
Match the method to the journey
Stability, temperature, and shipping are one decision, not three. Read the rest of the collection and logistics spokes to see how each kit format trades off against the others.