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PD CEN TS 16826 — Molecular In Vitro Diagnostic Examinations Pre-Examination Processes for Snap Frozen Tissue (Part 1 Isolated RNA; Part 2 Isolated Proteins)
Molecular In Vitro Diagnostic Examinations — Specifications for Pre-Examination Processes for Snap Frozen Tissue — Isolated RNA / Isolated Proteins
🧬 PD CEN/TS 16826 is a series of Published Documents issued by the British Standards Institution (BSI) based on the European Technical Specification CEN/TS 16826 for molecular in vitro diagnostic (IVD) examinations — pre-examination processes for snap frozen tissue. The reliability of molecular test results (e.g., gene-expression analysis, proteomic analysis) depends not only on the test method itself, but to a large extent on the pre-examination process — every step from tissue collection, snap freezing, storage and transport to nucleic-acid/protein extraction. The two parts in this batch, PD CEN/TS 16826-1:2015 (isolated RNA) and PD CEN/TS 16826-2:2015 (isolated proteins), specify the pre-examination process requirements for snap frozen tissue used in RNA and protein analysis respectively.
💡 The “pre-examination” stage is one of the main sources of error in molecular testing. If tissue is not snap frozen promptly after excision, stored improperly, or extracted non-standardly, RNA degrades and proteins are modified, directly causing false-negative or distorted results — exactly the core concern this series addresses.
1. Overview of the Series 📌
The CEN/TS 16826 series is prepared by the European Committee for Standardization (CEN) technical committee for in vitro diagnostics (CH/212, IVDs); the UK participates in its preparation and publishes it as a Published Document. The series takes snap frozen tissue as the analytical object and divides into parts by analyte type. The two parts in this batch are summarised below:
| Standard | Part Topic | Analyte | Year |
|---|---|---|---|
| PD CEN/TS 16826-1:2015 | Pre-examination processes — Isolated RNA | RNA extracted from snap frozen tissue | 2015 |
| PD CEN/TS 16826-2:2015 | Pre-examination processes — Isolated proteins | Proteins extracted from snap frozen tissue | 2015 |
⚠️ This series is for “snap frozen tissue” samples. Other sample types, such as formalin-fixed paraffin-embedded (FFPE) tissue, have their own pre-examination specifications (in the corresponding ISO/CEN series) and this series’ requirements should not be mixed with them.
2. Key Steps of the Pre-Examination Process 🧊
The pre-examination process for snap frozen tissue spans the whole chain from the operating room/sampling site to laboratory analysis, mainly comprising:
- Tissue collection and excision: representativeness of the sampling site, excision time and handling practice, minimising ischaemia time;
- Rapid freezing (snap freezing): rapid freezing by liquid nitrogen or similar to inhibit endogenous nuclease/protease activity and prevent RNA degradation and protein modification;
- Storage and transport: low-temperature storage (e.g., -80 °C or liquid nitrogen), cold-chain transport, avoiding repeated freeze-thaw;
- Extraction and quality control: RNA/protein extraction steps, purity and integrity assessment (e.g., RIN value, electrophoresis) and recording.
🚨 Repeated freeze-thaw is the biggest “silent killer” of snap frozen tissue samples: each freeze-thaw cycle further degrades RNA integrity and exacerbates protein degradation and modification. Samples should be aliquoted for single use and never repeatedly thawed and refrozen.
3. Part 1: Isolated RNA 🔬
PD CEN/TS 16826-1:2015 specifies the pre-examination process requirements for snap frozen tissue used for isolated RNA. Its content covers the operating requirements for tissue collection and snap freezing, storage conditions, RNA extraction practice, RNA quality assessment (purity, concentration, integrity and presence of inhibitors) and the corresponding recording and documentation requirements.
Because RNA is readily degraded by RNases, the standard particularly emphasises the operating environment (RNase-free), contamination-free assurance of consumables and reagents, rapid sample handling, and stability monitoring during storage, ensuring that the extracted RNA meets the quality requirements of downstream analyses (e.g., quantitative PCR, microarrays, high-throughput sequencing).
✅ For RNA, “the earlier the snap freezing, the faster the handling, the fewer the freeze-thaw cycles” is the golden rule. A standardised pre-examination process keeps RNA degradation to a minimum and significantly improves the authenticity and reliability of downstream results.
4. Part 2: Isolated Proteins 🧪
PD CEN/TS 16826-2:2015 specifies the pre-examination process requirements for snap frozen tissue used for isolated proteins. Protein analysis (e.g., Western blot, mass spectrometry, proteomics) is highly sensitive to protein degradation and post-translational modification, so the pre-examination stage is equally critical.
This part specifies tissue collection, snap freezing, storage, protein extraction (e.g., lysis protocols, use of protease inhibitors) and protein quality control (concentration, integrity, sample preservation), and considers the stability of post-translational modifications such as phosphorylation, providing a standardised basis for proteomic and biomarker research.
⚠️ The protein pre-examination process is often underestimated: metabolic changes and endogenous protease action after tissue excision rapidly alter the protein profile, especially dynamic modifications such as phosphorylation. Standardised snap freezing and extraction are prerequisites for reproducible proteomics results.
5. Key Technical Requirements and Quality Management 📋
Combining the two parts, the key technical requirements for the snap frozen tissue pre-examination process include:
- Time window from excision to snap freezing: after collection, tissue should be snap frozen as soon as possible (ideally within minutes), with key time points recorded;
- Snap freezing method: liquid nitrogen or low-temperature medium, suitable sample volume, ensuring rapid, uniform internal cooling;
- Storage and cold chain: long-term storage at -80 °C or in liquid nitrogen, cold-chain transport with temperature monitoring, avoiding freeze-thaw;
- Extraction practice: RNA/protein extraction per validated protocols, controlling enzymatic action and contamination;
- Quality assessment and recording: assess extract quality and record completely to ensure traceability.
6. Clinical and Research Applications 🏥
This series mainly serves:
- Tumour molecular diagnosis: gene-expression profiling, mutation and fusion-gene detection based on snap frozen tumour tissue;
- Biomarker research: extracting RNA/proteins from snap frozen tissue for biomarker discovery and validation;
- Translational medicine and clinical trials: standardising sample collection in multicentre studies for cross-centre comparability;
- Biobanking: standardised collection, storage and quality grading of snap frozen tissue supporting long-term cohort studies.
💡 Implementation advice: clinical and research institutions should write the pre-examination specification into sample-collection standard operating procedures (SOPs), train sampling personnel, and record key time points (collection, snap freezing, storage); establish sample quality files to provide quality evidence for downstream molecular testing.
7. Frequently Asked Questions ❓
❓ Q: Why is snap frozen tissue commonly used for molecular testing?
A: Snap freezing maximally preserves the original state of nucleic acids and proteins in tissue, avoiding chemical modification and degradation caused by fixation/embedding, and is better suited to molecular analyses with high RNA/protein quality requirements.
A: Snap freezing maximally preserves the original state of nucleic acids and proteins in tissue, avoiding chemical modification and degradation caused by fixation/embedding, and is better suited to molecular analyses with high RNA/protein quality requirements.
❓ Q: Why is RNA analysis so sensitive to the pre-examination process?
A: RNA is readily degraded by the ubiquitous RNases, and degradation is fast. Excision time, snap-freezing delay and repeated freeze-thaw all cause RNA fragmentation, directly affecting the accuracy of quantitative PCR and sequencing results.
A: RNA is readily degraded by the ubiquitous RNases, and degradation is fast. Excision time, snap-freezing delay and repeated freeze-thaw all cause RNA fragmentation, directly affecting the accuracy of quantitative PCR and sequencing results.
❓ Q: What is the difference between Parts 1 and 2?
A: Part 1 is for RNA analysis and Part 2 for protein analysis. They agree on basic steps such as collection, snap freezing and storage, but differ in emphasis on extraction, quality assessment and stability (RNA integrity vs protein degradation and modification).
A: Part 1 is for RNA analysis and Part 2 for protein analysis. They agree on basic steps such as collection, snap freezing and storage, but differ in emphasis on extraction, quality assessment and stability (RNA integrity vs protein degradation and modification).
❓ Q: How do you judge whether extracted RNA/protein quality is acceptable?
A: RNA is usually judged by RIN value/electrophoretic integrity combined with purity (A260/A280); protein by concentration measurement, electrophoretic integrity, and degradation/modification detection. Specific indicators should be determined with the test method and standard requirements.
A: RNA is usually judged by RIN value/electrophoretic integrity combined with purity (A260/A280); protein by concentration measurement, electrophoretic integrity, and degradation/modification detection. Specific indicators should be determined with the test method and standard requirements.
❓ Q: Does this specification apply to FFPE tissue samples?
A: No. FFPE tissue has its own pre-examination/testing process specifications; the sample type is different and the handling and quality requirements differ, so the corresponding standards should be followed.
A: No. FFPE tissue has its own pre-examination/testing process specifications; the sample type is different and the handling and quality requirements differ, so the corresponding standards should be followed.