The right temperature for biological sample storage depends on three things: the sample type, how long you need to keep it, and what you will analyse later. As a rule of thumb, use +4 °C for hours to days, –20 °C for robust DNA, –80 °C for serum, plasma and RNA over years, and below –135 °C for anything that must stay viable, such as cells and tissue.
That rule of thumb is a starting point, not a storage policy for a biobank or a clinical trial. Every temperature tier carries its own risks: freeze-thaw cycles in auto-defrost freezers, slow degradation at –80 °C, recrystallisation above the glass transition temperature. This guide matches the five common temperature tiers to the main sample types and shows when it pays to move into cryogenic storage with liquid nitrogen (LN₂).
Biological material keeps changing as long as water inside it can move. Enzymes such as RNases and proteases remain partly active at –20 °C, and oxidation and hydrolysis continue slowly even in the frozen state. The lower the temperature, the slower these processes run.
The critical threshold is the glass transition temperature of water, at roughly –135 °C. Below it, the remaining unfrozen fluid solidifies into a glass-like state. Molecular movement practically stops, ice crystals no longer grow and biological activity ceases. That is why cryopreservation follows one simple rule: living cells belong below –135 °C for long-term storage. Our article on the physics of storage at –196 °C explains how this state forms.
Temperature stability matters as much as the set point. Every excursion, for example from frequently opening a freezer door, can let ice crystals grow. Every full freeze-thaw cycle damages proteins, fragments nucleic acids and lowers post-thaw cell viability. Good sample storage therefore always means aliquoting, planning access and monitoring temperatures continuously.
The refrigerator is a waypoint, not a store. It suits whole blood, urine or swabs between collection and processing, usually for hours to a few days depending on the assay and your pre-analytical requirements.
Standard –20 °C lab freezers are adequate for purified DNA in buffer for months to a few years, and for many reagents. They are not suitable for RNA, proteins that must keep their activity, or living cells. Watch out for auto-defrost (frost-free) models: their defrost cycles warm samples repeatedly, which acts like partial thawing.
The ultra low temperature freezer is the workhorse of most labs. Serum, plasma, purified DNA and RNA, protein extracts and bacterial glycerol stocks can be held at –80 °C for years, and stability for many routine analytes is well documented. For sensitive biomarkers, verify stability for the specific analyte, because slow degradation still continues at –80 °C.
Living cells tolerate –80 °C only briefly, typically for the first days after freezing. Long term, –80 °C sits above the glass transition temperature and viability declines week by week. Our comparison ULT freezer vs. cryogenic tank shows when an ULT freezer is enough and when a tank is the better choice.
At –150 °C or colder, the –135 °C threshold is reliably undercut. Mechanical –150 °C freezers reach this tier, and so does the vapour phase above liquid nitrogen. Depending on height and tank design, vapour-phase temperatures typically range from about –150 °C to –190 °C. Vapour-phase storage avoids direct contact with liquid nitrogen and with it the risk of cross-contamination through the LN₂.
In the liquid phase, samples sit directly in nitrogen at –196 °C. This offers the largest thermal reserve but requires suitable, tightly sealed containers so nitrogen cannot leak in. Our article on vapour phase vs. liquid phase storage covers which phase suits which application.
The following overview summarises common recommendations from biobanking practice, such as the ISBER Best Practices. Your study protocol and planned analyses always take precedence.
DNA
RNA
Serum and plasma
Living cells (stem cells, PBMCs, cell lines, cell therapy products)
Tissue
In clinical research, storage conditions become part of the trial data. Our article on proper sample storage in clinical trials explains what that means for sponsors and sites.
Duration matters as much as sample type. Three questions help you pick the tier:
How long will the sample be kept? Weeks to a few years at –80 °C are uncritical for many analytes. For cohort and longitudinal studies running 10, 20 or 30 years, cryogenic storage is the safer choice, because tomorrow's assays are not known today.
Must the sample stay viable? Then there is no alternative to temperatures below –135 °C.
How critical is a failure? An ULT freezer warms up within hours after a power cut or compressor fault. A vacuum-insulated LN₂ tank needs no electricity for cooling and holds its temperature for an extended period even without refilling. That buys valuable response time in an emergency.
For irreplaceable samples, the third point is often decisive. Many biobanks therefore combine both: –80 °C for working aliquots that are accessed often, and the LN₂ vapour phase for reserve samples and long-term collections. Similar trade-offs apply in pharma, as our guide to vaccine and biologics storage shows.
Anyone storing samples for research, diagnostics or clinical trials must be able to prove that each sample was kept under the defined conditions.
In practice that means qualified storage equipment, continuous temperature recording, alarm chains with escalation, a contingency plan with backup capacity and an unambiguous link between every sample and its storage position.
Consarctic® is a market-leading German manufacturer of cryogenic systems for the life sciences and covers the tier below the glass transition end to end, from freezing to monitoring:
Find out more about our solutions for biobanking and cryopreservation. Consarctic® works to ISO 9001:2015 and EN ISO 13485:2016 and serves more than 1,500 customers in over 30 countries, including Qatar Biobank, the German Red Cross and Charité Universitätsmedizin Berlin.
Living cells should be stored long term below the glass transition temperature of about –135 °C, in practice usually in the vapour phase above liquid nitrogen at roughly –150 °C to –190 °C. At –80 °C, cells last only a few days before viability drops noticeably.
For purified RNA, –80 °C is usually sufficient for years, provided samples are aliquoted and not thawed repeatedly. For tissue intended for later RNA extraction, and for long-term biobanks, storage below –135 °C offers a wider safety margin.
Many routine serum analytes are stable at –80 °C for years. Stability depends on the individual analyte, however. For sensitive biomarkers or very long studies, verify it, or store the samples in the LN₂ vapour phase from the outset.
In the liquid phase, samples sit directly in nitrogen at –196 °C. In the vapour phase, they are stored above it in cold nitrogen vapour. The vapour phase avoids cross-contamination through the LN₂ and is now standard in many biobanks.
Good sample storage starts with a clear assignment: which sample, for how long, for which analysis? Answer those questions and the right temperature tier follows, protecting samples that often cannot be collected a second time.
Which of your samples should already be stored below –135 °C? Talk to the experts at Consarctic®. We plan, supply and qualify your cryogenic storage as one integrated system.