Product shelf life is an essential product performance requirement that, along with other design requirements, is used to determine the safety and efficacy of a clinical diagnostic reagent, whether they are made by a laboratory or commercially produced. Product shelf life can be determined following various domestic and international guidance documents.
In this article, we provide a high-level overview of how product shelf life is determined and how accelerated stability studies can be used to estimate product shelf life. We also discuss some of the limitations and key considerations labs should consider before using an accelerated stability model to estimate shelf life for lab-developed reagents.
The discussion also will help laboratory employees understand how their suppliers determine the shelf life of products, which has the potential to impact test results.
Product expiration date
Establishing the expiry date (expiration or shelf life) for in vitro diagnostic products — such as reagent kits, calibrators, and quality controls — is a key quality and regulatory requirement for these products and is required by national and international regulatory agencies.
Since laboratory developed tests (LDTs) may be subject to these design control requirements, laboratories also need to demonstrate that specified design requirements, such as shelf life and stability, are also met during the design verification process. (LDTs are assays that are intended for clinical use and are designed, manufactured, and used within a single laboratory.)1
The expiration date shown on the product label, as well as the instructions for use (IFU), indicate that the product will perform as designed and was developed to meet product design requirements and user needs within the time period — from the manufacturing date to the expiration date (last day of use).
There are several domestic and European standard and guidance documents providing recommendations and direction on how to design and execute stability experiments to generate the necessary stability data, which could be used to establish shelf life at the recommended storage conditions for these products. For example, the Clinical and Laboratory Standards Institute (CLSI) documents for EP25-A2 and EN ISO 23640,3 provide guidance on the establishment and verification of shelf life stability claims for quantitative and qualitative in vitro diagnostic products.
There are typically three questions that need to be answered for defining stability:
1) Which product characteristics/metrics are considered key performance indicators?
2) What are the acceptance criteria or changes for each characteristic/metric that can be tolerated?
3) What is the statistical confidence level required for analyzing stability results?
Since each of these characteristics is different for various diagnostic reagents, it is not practical to provide a single protocol that is appropriate for all diagnostic products. For example, the stability acceptance criterion for a calibrator, quality control and a wash buffer of a reagent kit are very different and may vary from ±1% to ±20% of the initial value for the key measurement of these products. The appropriate sample size and statistical confidence level may also vary, depending on the intended use of the reagent.
Appropriate statistical methodology (for example, detection of outliers, determination of replicate runs, etc.) should be used to ensure that quality results are generated for shelf life stability determinations. Therefore, manufacturers of diagnostic reagents, as well as laboratory professionals involved in development of reagents for LDTs, should establish standard operating procedures for performing stability studies consistent with guidance and standardization documents, such as CLSI EP25-A and EN ISO 2346, and select and monitor physical, chemical, biological, or microbiological properties of the product in which their changes (for example, potency, activity, or concentration) impact the product shelf life and ultimately the safety and efficacy of the product.
Stability studies for shelf life determination
Expiry dates are assigned to in vitro diagnostic reagents, calibrators, quality controls, and other components by the manufacturer based on experimentally determined stability properties. Typically, two approaches can be used to generate the stability data necessary to establish an expiration date for a diagnostic reagent.
Real time stability studies can be done by storing the reagent at its recommended storage temperature and regularly sampling and testing the reagent at defined timepoints and periods of time, typically 20% longer than the desired expiration date. For example, for a reagent with a desired shelf life of 1 year, the reagent may be tested weekly or monthly for 14 months (2 months past the desired shelf life). On the other hand, accelerated stability studies can be designed and performed at elevated temperatures compared to normal storage conditions for products, or the storage temperature on the product label, to observe changes in product performance, mainly stability, more rapidly than what would be seen under normal storage conditions.
For example, a product with a storage temperature of 2-8°C can be exposed to temperatures such as 35°C or 45°C to accelerate the degradation process. Since many diagnostic reagents have long shelf lives, in the order of 1 to 3 years, the shelf lives for these products are first estimated with accelerated stability studies during the product development process, which usually take several weeks, and are later supported with real-time stability studies that require several years.
Accelerated stability studies are based on the Arrhenius Equation, which describes the mathematical relationship between the rate constant of a chemical reaction, the reaction temperature, and the activation energy for the molecule under study.4 Generally, for every 10-degree rise in temperature (°C), the reaction rate doubles. Therefore, by increasing the temperature at which the product is stored, you can increase the reaction rate and degradation rate of a molecule or a product. For example, assuming an activation energy of 20 kcal/mole/degree, storing a product at 35 °C for 30 days is approximately equivalent to storing the same product at 5 °C for 3 years, in terms of degradation rate.
Key considerations when designing accelerated stability studies
In a recent article, some of the limitations of accelerated stability studies were highlighted.5 Exposure of reagents to raised temperatures during an accelerated stability study may create conditions and chemical environments that produce degradation in the product. However, this degradation may not be observed during a real time stability study when the product is stored under normal and unstressed storage conditions. This is especially true when the normal storage temperature of the product is at -10°C or lower, which means the product is frozen and is in a solid state, and accelerated stability studies are performed at higher temperatures (for example, 35°C), which means the product is now in the liquid state. For this reason, the prediction from the accelerated stability model may not be accurate and may result in overestimation or underestimation of shelf life.
Some other factors that may result in poor agreement between real time and accelerated stability studies are increased solubility and evaporation due to exposure of a reagent to higher temperatures, susceptibility of certain measurands to photodegradation more than thermal degradation, changes in residual moisture in lyophilized reagents, increased or decreased proteolytic and enzymatic activities of liquid reagents due to exposure to raised temperatures, and changes in pH of the reagent due to escaping of dissolved gases and organic volatiles such as carbon dioxide, oxygen, and alcohols.
Generally, accelerated stability studies predict stability and shelf life accurately, and there is reasonable and acceptable agreement between the actual shelf life from real time stability studies, which are performed over several years, and the estimated shelf life from accelerated stability studies, which are performed in a shorter period of time, typically over a few weeks. However, exposure of reagents to elevated temperatures during the accelerated stability study may create conditions and chemical environments that produce degradation in products that may not be typically observed during real time stability studies when the product is stored under normal and unstressed storage conditions.
Product developers and labs should assess the applicability and suitability of the accelerated stability studies for their products by performing a few simple and fast experiments and consider the shortcomings of the accelerated stability studies prior to fully utilizing the model to estimate or establish product shelf life. For example, designing and executing pre-accelerated stability experiments, by storing key components of a reagent such as the liquid buffer system at the recommended storage temperature of the product and also at its equivalent raised temperature (for example, 9 days at 5°C which is approximately equivalent to 6 hours at 35°C) and comparing a key chemical parameter such as pH for the two conditions may provide insight into if the raised temperature used in the accelerated stability studies creates a change in pH that is not normally observed during real time stability studies. The results of the rapid study may suggest that the accelerated model may not be appropriate for estimating shelf life for a reagent and, consequently, will avoid an accelerated stability study with poor predictive value.
- CLSI QRSLDT, Quality System Regulation for Laboratory Developed Tests: A Practical Guide for the Laboratory, January 2015.
- CLSI EP25-A, Evaluation of Stability of In Vitro Diagnostic Reagents; Approved Guideline, September 2009.
- EN ISO 23640, In Vitro Diagnostic Medical Devices - Stability Testing of In Vitro Diagnostic Reagents, November 2009.
- Tinoco JR, Sauer K, Wang JC. Physical Chemistry: Principles and Applications in Biological Sciences, 1st Ed. New Jersey: Prentice Hall; 1978: 294-7.
- Ebrahim A, DeVore K, Fischer T. Limitations of Accelerated Stability Model Based on the Arrhenius Equation for Shelf Life Estimation of In Vitro Diagnostic Products. Clin Chem, 67, 684-688 (2021).
FDA guidance on using expired lab products
By MLO Staff
The U.S. Food and Drug Administration (FDA) offered guidance on the use of expired products in October 20211 due to shortages during the COVID-19 pandemic. Many critical supplies weren’t available due to supply chain shortages, shipping delays and manufacturing problems, but testing needed to continue.
Throughout the COVID-19 response, laboratories have faced limited reagent, kit and material inventories, with some reagents approaching or passing expiration dates. The FDA offered guidance, saying that critical supply shortages may necessitate the use of expired reagents to maintain testing.
According to the FDA, a medical product is typically labeled by the manufacturer with an expiration date. This reflects the time period during which the product is expected to remain stable, or retain its identity, strength, quality, and purity, when it is properly stored according to its labeled storage conditions.
In some cases, testing has shown that certain properly stored medical products can be used beyond their labeled expiration date if they retain their stability. The FDA is engaged, when appropriate, in various expiration dating extension activities.
During the COVID-19 public health emergency, the Centers for Disease Control and Prevention (CMS) will allow laboratories to use expired COVID-19 test kits, reagents and swabs, as long as the appropriate testing and documentation is maintained and the manufacturer’s instructions do not prohibit use of the expired material (see CMS FAQ #27 [12-17-2020]) (CMS, 2020).2 This guidance stated, “When in-date reagents are unavailable, it may become necessary to frame written policies for their temporary use beyond their expiration dates until non-expired supplies become available. Under no circumstances, however, should a laboratory adopt policies that would allow for the regular use of expired reagents.” Thus, laboratories may use expired supplies until non-expired supplies become available provided that they put policies and procedures in place to ensure the reagents are performing as expected (e.g., ensuring that any expired supplies pass quality control tests with each assay run).
Guidance offered by the FDA
The FDA says laboratories should establish written policies and procedures regarding use of expired reagents, and consider the following key points
- When possible, request that the manufacturer provide a letter of expiry extension for the reagent or test kit, or document in writing that the manufacturer would vouch for the accuracy and reliability of the reagents while in use past the expiration date.
- Place these letters in the laboratory’s reagent QC binders. It is important to note that regardless of CMS enforcement discretion, laboratories remain responsible for ensuring the accuracy of their test results.
- Setting expiration dates is historically the manufacturer’s responsibility. Expiration date establishment requires considerable effort, particularly for a testing laboratory during a pandemic.
Expiration date practices are outlined in: CLSI EP25-A Evaluation of Stability of in vitro Diagnostic Reagents and Approved Guideline and ISO EN 13640, Stability Testing of in vitro Diagnostic Reagents.
If using expired reagents in a laboratory, QC must be closely monitored and consider doing additional QC. Shortages of supplies and reagents may necessitate additional verifications or validations to add new specimen types, media types or other testing components.