Technical Roadmap and Quality Control Key Points for Liquid Biopsy Reagents

Main Targets and Detection Strategies of Liquid Biopsy Reagents

Liquid biopsy reagents typically use body fluid samples such as blood, urine, and pleural or peritoneal effusion as test specimens, focusing on targets including circulating tumor DNA (ctDNA), circulating tumor cells (CTC), exosomes, and circulating RNA. Different targets have differing requirements for sample preservation, enrichment methods, nucleic acid extraction efficiency, and detection sensitivity. For example, ctDNA in plasma has shorter fragments and lower abundance, generally requiring high-efficiency cell-free nucleic acid extraction reagents combined with high-fidelity library preparation or digital PCR protocols; CTC detection relies more on cell enrichment and identification reagents, and common specifications focus on recovery rate, purity, and the ability to maintain cell viability.

From the perspective of technical approaches, liquid biopsy reagents can be classified into PCR-based, digital PCR-based, high-throughput sequencing (NGS)-based, and immunocapture-based types. NGS-based kits typically include library preparation, targeted capture, and sequencing ancillary components, suitable for parallel analysis of multiple genes and loci; digital PCR reagents emphasize absolute quantification capability, suitable for low-frequency detection of known mutations. Selection should be matched according to the laboratory platform, sample volume, and analytical objectives.

Key Technical Indicators of ctDNA Detection Reagents

For ctDNA liquid biopsy reagents, nucleic acid extraction efficiency and fragment recovery capability are common points of focus. Reagents are generally required to stably recover short-fragment cell-free DNA while reducing interference from high-molecular-weight genomic DNA. In the library preparation step, adapter dimers, amplification bias, and base error rates need to be controlled, and sequencing depth and analytical sensitivity should be evaluated in conjunction with specific applications. For digital PCR reagents, attention should be paid to droplet generation stability, fluorescence signal discrimination, and lot-to-lot consistency.

In performance evaluation, laboratories typically refer to indicators such as the limit of detection, precision, accuracy, analytical specificity, and interference resistance. It should be noted that these indicators are not fixed and are greatly influenced by sample type, pre-processing workflow, and detection platform, and should be monitored through internal quality control and regular calibration.

Quality Control System and Standardization Challenges

Quality control of liquid biopsy reagents runs through the entire process of sample collection, transport, extraction, detection, and data analysis. The choice of anticoagulants and cell-free DNA preservatives in collection tubes, sample centrifugation conditions, and freezing temperature and duration can all affect test results. A common practice is to establish standard operating procedures, use positive quality control materials, negative quality control materials, and blank controls, and record lot numbers and operating parameters.

The industry currently still faces challenges such as a lack of reference materials and insufficient comparability of results between different laboratories. Promoting the standardization of automated extraction, closed-system library preparation, and data analysis workflows can help reduce human error. Relevant companies should pay attention to industry standards and regulatory requirements, clearly state the intended use, sample requirements, and performance boundaries in labeling, and avoid overstating the scope of application.