Multiplex PCR
amplification and detection of multiple targets in the same reaction. Performance depends on the balance between primers, probes, enzymes, controls and operating conditions, with particular attention to the weakest targets.

Ambient-stable
a stability claim relating to a product or component within a defined temperature range, duration and packaging conditions. It does not mean that the product can be stored without limits.

Cold-chain-free
a condition applicable only when all components and stages covered by the claim require no refrigerated transport or storage. Stability of the master mix alone does not automatically make the entire kit cold-chain-free.

Shelf life
the period during which the finished, sealed product, stored under the stated conditions, maintains performance within defined specifications.

Shipping stability
the product’s ability to maintain integrity and performance under the anticipated transport conditions, including defined temperature excursions.

In-use stability
stability after the product has been opened, reconstituted or loaded, for the stated period and under the stated operating conditions.

In molecular diagnostics, stability is often described as a property of the reagent. For a multiplex PCR panel, however, it is the outcome of a system: multiple primers and probes share the same reaction, controls must remain reliable, and targets close to the limit of detection cannot afford to lose margin. A mixture that withstands drying and works at time zero is not, by itself, an ambient-stable product.

The issue therefore extends beyond formulation alone. When performance depends on temperature, transport, storage and the management of excursions become part of the analytical method. Broadening the temperature window can reduce this dependence and make shipping, inventory and operational continuity more flexible, but the benefit exists only within demonstrated conditions and only if the vulnerability is not transferred to the packaging, reconstitution, sample, controls or operator.

This Insight therefore distinguishes technological feasibility from product stability, assay robustness and logistical value. Its aim is not to identify one universally superior stabilisation technique, but to clarify what evidence enables the transition from a promising formulation to a defensible claim. In multiplexing, the final criterion is not shelf life alone: it is the preservation of sensitivity, specificity, controls and interpretability throughout production, distribution and use.

The journey of a PCR test begins before the thermocycler, with the production of raw materials, and continues through formulation, lot release, packaging, transport, receipt, storage, preparation and use. If performance depends on maintaining controlled temperatures, refrigerators, freezers, coolants, data loggers and excursion procedures become extended parts of the method.

Deterioration does not necessarily coincide with complete failure. It can appear as increased Cq values, reduced fluorescence intensity, greater dispersion between replicates, more repeat tests or loss of detection close to the analytical limit. In multiplexing, the effect can be even less apparent: an abundant target continues to produce a convincing signal while a rare target or the internal control loses margin. The run appears valid, but the panel’s information capacity has changed.

A formulation capable of broadening the temperature window therefore addresses a genuine vulnerability. To assess its benefit, it is necessary to specify which dependence is reduced, for how long and under which conditions, and then verify the consequences for the rest of the workflow.

A temperature-controlled warehouse, a room without humidity control and a vehicle standing in the sun do not represent the same environment. The term ambient-stable is informative only when accompanied by a temperature range, duration, validated packaging and, where relevant, tolerated humidity and excursions. The stages must also remain distinct: shelf life concerns the finished, sealed product stored under the stated conditions; shipping stability describes transport; and in-use stability begins after opening, reconstitution or loading.

A product may tolerate a brief temperature peak during shipment without having a multi-year shelf life at that temperature. In a system described by Thirion and colleagues, a lyophilised matrix containing primers and probe maintained performance after four days at 37 °C and, once reconstituted, for at least two weeks at 4 °C [1]. These are two distinct bodies of evidence concerning different stages; moreover, the study concerns an oligonucleotide matrix, not an entire master mix.

Defining a system as cold-chain-free requires an indication of which components the claim covers. If the master mix is stable but a control, diluent, sample or extraction reagent remains thermolabile, dependence on the cold chain has been reduced, not eliminated. The result must therefore be attributed to the component concerned, without extending that property to the entire kit.

Lyophilisation is the best-known approach. Water is removed through freezing, sublimation and secondary drying; sugars such as trehalose can help preserve protein structure and form an amorphous matrix, while excipients such as mannitol can support the physical structure. The outcome nevertheless depends on the interaction between formulation, cycle and container. In a study of Taq polymerase and master mix, trehalose, mannitol and process conditions proved critical to preserving activity after exposure to 37 °C and controlled relative humidity [2].

Freezing can cause local solute concentration, pH changes, precipitation or phase separation. Alternative processes are therefore being explored. In 2026, Renu and colleagues compared a lyophilised probe-based qPCR mixture with a formulation stabilised by capillary-assisted vitrification, which avoids the freezing stage. In the proof of concept, the two solutions showed comparable performance and stability under the conditions studied; vitrification provided faster recovery and accommodated a glycerol-containing formulation [3]. The work concerns a single DNA assay for Mpox, using proprietary buffers and supports, and does not demonstrate general superiority.

At least four verification stages lie between a mixture that withstands drying and a ready-to-use product. The first concerns the molecule: enzymes, oligonucleotides, nucleotides and labels must preserve their structure and function. Next comes the dry format — residual moisture, amorphous or crystalline state, cake or bead integrity, and reconstitution — which is already inseparable from the container-closure system. Only then can the assay be assessed for its ability to maintain sensitivity, specificity, precision, efficiency, controls and target balance. The final verification is operational: how the product responds to transport, opening, instruments, operators and anticipated deviations.

Passing one verification does not resolve the next. Enzyme activity is not sufficient to establish panel reliability; performance at time zero is not sufficient for industrialisation; and good stability in the packaging can be undermined by variable reconstitution. The target product profile must therefore precede the choice of technology. Geometry, volume, container, reconstitution times, manufacturing process and context of use define the product more than the label applied to the technology.

Enzyme, nucleotides, salts and reaction space are shared by multiple primer and probe systems. This sharing creates unwanted interactions, competition between targets and dependence on finely balanced concentrations. To remain interpretable, the dried panel must preserve both the individual components and the functional proportions that keep them in balance.

MIQE 2.0 recommends demonstrating that multiplexing produces results consistent with the corresponding singleplex analyses, and characterising efficiency, linearity, dynamic range, limits of detection and quantification, and controls [4]. After stabilisation, comparability should include samples close to the LoD, target combinations, multiple positivities, matrices containing inhibitors, and variability between lots, instruments and sites. A stable mean can conceal the selective loss of the very target that determines the value of the panel.

A sample-ready multiplex qPCR assay for malaria showed performance comparable to the liquid formulation and stability at 37 °C for 42 days in the system evaluated; some differences emerged at low concentrations [5]. A different level of evidence comes from the thermostabilised triplex PCR for Vibrio cholerae: it included an internal control and offered performance comparable to the conventional method, but stability of approximately seven months at 24 °C was estimated using the Q10 method rather than being supported solely by real-time data [6]. Published studies therefore describe different levels of maturity.

The 2026 work on lyophilised beads for six pathogens combines rapid lysis with software-assisted classification of melting profiles. Five lots, precision and interference studies, accelerated stability testing and 210 clinical samples showed high agreement with the comparators; on the same dataset, software classification matched manual interpretation [7]. Its scope remains limited by the constraints declared by the authors — a single-centre study and few positive samples for some targets — and supports that specific system. It does not authorise generic claims about automated interpretation, artificial intelligence or clinical performance in other contexts.

In the case studied by Drzewnioková and colleagues, a lyophilised qRT-PCR reagent was used in four veterinary laboratories in sub-Saharan Africa. Performance for avian influenza and rabies was broadly comparable with that of liquid reagents; the differences observed for some divergent lyssaviruses depended on complementarity between the oligonucleotides and target sequences [8]. The project simplified logistics without removing performance from the constraints of assay biology. The field evidence concerns that product and cannot automatically be transferred to the entire technology class.

A pre-aliquoted mixture can reduce pipetting, master-mix preparation, contamination and variability between operators. The operational advantage depends on rapid and uniform reconstitution after adding a defined volume of sample or diluent. Reintroducing the water removed during production, however, creates a new critical sequence: volume, order of addition, waiting time, mixing, centrifugation and complete dissolution.

In the comparison by Renu and colleagues, the vitrified sample was recovered in less than one minute; the lyophilised cake required the addition of water, vortexing, centrifugation, incubation and further mixing [3]. This limitation belongs to the system studied, not to lyophilisation in general, and shows why the workflow must be measured rather than assumed. In miniaturised systems, where uniform distribution is even more important, Xie and colleagues showed that controlled rehydration of prestored reagents was necessary to achieve robust performance across reaction chambers in a multiplex digital PCR architecture [9]. The technology differs from conventional qPCR, but the design lesson remains relevant.

Usability testing should include representative operators, realistic volume errors, shortened or extended timings, incomplete mixing, training consistent with the context and anticipated environmental conditions. A format that eliminates the freezer but requires delicate reconstitution has shifted complexity without necessarily reducing it.

In a dry product, packaging enters the stability profile from the point of moisture control. Residual water and headspace interact with material permeability, closure integrity and desiccants; for specific components, including certain fluorescent probes, light and oxygen add further considerations. The unit to validate is therefore the finished product in its final container, not the freshly dried mixture. Even with an unchanged formulation, changing the tube, pouch, seal or supplier can alter the outcome.

Accelerated studies are used to compare formulations, identify degradation mechanisms, select packaging and support an initial claim. Shelf life nevertheless requires an appropriate extrapolation model and real-time confirmation, because phenomena other than those observed under ordinary conditions can predominate at elevated temperatures.

Within the European IVD framework, Regulation (EU) 2017/746 distinguishes shelf life, in-use stability and transport stability. For shelf life, it requires data from at least three lots manufactured under conditions substantially equivalent to routine production; it allows accelerated or extrapolated data for initial claims, accompanied by real-time follow-up. Transport stability must consider foreseeable conditions, including extremes of heat and cold [10]. ISO 23640:2011 and CLSI EP25, second edition, provide further references for planning, analysing and documenting stability studies [11–12].

In a mature programme, product definition advances alongside the evidence. It begins with the use profile, which identifies users, matrices, instruments and the logistics pathway. The final configuration translates that profile into formulation, volume, container, closure and instructions; a comparative baseline then enables the effects of stabilisation to be measured. On this basis, real-time and accelerated studies follow multiple lots and verify end-of-life performance, with particular attention to weak targets, controls, co-positivities and critical matrices. Transport, opening, reconstitution and error tolerance complete the validation.

Validation does not end with the first claim. Changes in raw material, supplier, process or packaging may require reassessment; data from production lots and post-market trends verify the continuing validity of the initial assumptions. Labelling also contributes to performance: the storage range, expiry, reconstitution and conditions of use must enable the operator to remain within the demonstrated scope.

With a validated window compatible with the network, the critical component opens up more operational options. Shipments may require fewer coolants and fewer strictly timed deliveries, while a site can hold stock without occupying freezer capacity. Deviations covered by the demonstrated conditions are managed using predefined criteria and quality procedures rather than as indeterminate events. Finally, a pre-aliquoted format can reduce preparation steps and contamination risk.

Shipments with excursions, quarantined lots, release time after a deviation, waste, lead time, stock coverage, emergency reorders, test availability by site and repeat tests make the benefit observable. These indicators describe resilience at the operational level and must be interpreted alongside the remaining constraints: samples, controls, diluents or extraction reagents may have different windows; instruments, training, traceability and governance continue to determine network reliability.

The same format can have very different value depending on the use case. Removing dry ice from the master mix has little impact if the sample must still reach a central laboratory quickly. Where samples and reagents can be handled at decentralised operating sites, the same change can instead affect turnaround times, inventory and service continuity. The relevant comparison is therefore between dependencies removed and dependencies remaining, not the ambient-stable label.

For TCO and sustainability, the scope remains the complete system. Less refrigerated transport may reduce insulated packaging, coolants, monitoring and excursion management, while also enabling consolidated shipments or more flexible inventory. Conversely, manufacturing, fill-finish, the drying cycle, high-barrier packaging, desiccants, quality control, shipped mass, yields and waste can shift costs and impacts between upstream and downstream activities. A route-specific model is therefore necessary to assess savings; broader environmental claims also require a life-cycle assessment with declared boundaries. Without these steps, the benefits remain possible, not universal.

Between promising chemistry and a validated workflow, progress is made through successive claims that a single label cannot compress. Prototype stability guides formulation and process without yet changing the logistics instructions. Tolerance of a defined shipment can simplify that route, but does not by itself demonstrate an ambient shelf life. Even a stable master mix eliminates one specific dependence; the kit may retain others.

Four questions define the decision: what is the exact unit covered by the claim? Which conditions and stages have been tested? What performance is maintained at the end of shelf life? Which bottleneck disappears in the actual use case? A vague answer requires equal caution in formulating the benefit. Only a fully demonstrated pathway allows ambient-stable to be applied to the system rather than to the formulation alone.

For a multiplex panel, ambient stability is demonstrated when the finished product preserves its analytical profile throughout production, distribution and use. Formulation and process are the starting point; packaging, reconstitution and behaviour at the end of shelf life determine whether that performance reaches the laboratory or operating site intact.

A dry format can remove one logistical constraint and create others, from moisture and behaviour at the end of shelf life to the human factor or other kit components. Shelf life therefore describes one part of the outcome; the most useful measure remains the accuracy and interpretability maintained in the real workflow.