Subpar reporting of pre-analytical variables in RNA-focused blood plasma studies

Extracellular RNA (cell-free RNA; exRNA) from blood-derived liquid biopsies is an appealing, minimally invasive source of disease biomarkers. As pre-analytical variables strongly influence exRNA measurements, their reporting is essential for meaningful interpretation and replication of results. The aim of this review was to chart to what extent pre-analytical variables are documented, to pinpoint shortcomings and to improve future reporting. In total, 200 blood plasma exRNA studies published in 2018 or 2023 were reviewed for annotation of 22 variables associated with blood collection, plasma preparation, and RNA purification. Our results show that pre-analytical variables are poorly documented, with only three out of 22 variables described in over half of the publications. The percentage of variables reported ranged from 4.6% to 54.6% (mean 24.84%) in 2023 and from 4.6% to 57.1% (mean 28.60%) in 2018. Recommendations and guidelines (i.e., BRISQ, ASCO-CAP, BloodPAC, PPMPT, and CEN standards) have currently not resulted in improved reporting. In conclusion, our results highlight the lack of reporting pre-analytical variables in exRNA studies and advocate for a consistent use of available standards, endorsed by funders and journals.

Abstract B49: Substantial performance differences among RNA purification kits and blood collection tubes in the Extracellular RNA Quality Control study—important considerations for liquid biopsies

Cancer biomarker studies require procedures that provide accurate and precise test results with high analytical sensitivity. Consequently, the growing use of extracellular RNA from human biofluids as clinically relevant biomarker requires the implementation of benchmarked methods for sample collection, processing, and profiling. While several small-scale studies have pointed at the impact of individual preanalytical factors, no comprehensive study has addressed the many preanalytical variables affecting downstream sequencing of blood-derived exRNAs. In the Extracellular RNA Quality Control study, we have systematically evaluated the type of blood collection tube (n=10, including 5 so-called preservation tubes), the time between blood draw and plasma preparation (n=3), different plasma types (n=3, i.e., platelet-free, -poor, and -rich plasma), and RNA purification methods using the supplier-specified minimum and maximum plasma input volumes (n=15). The impact of these preanalytical factors is assessed by deep transcriptome profiling of all small and messenger RNAs from healthy donors’ plasma, using TruSeq Small RNA sequencing and TruSeq RNA Exome sequencing, respectively. All experiments are conducted in triplicate (for a total of 270 transcriptomes) using 191 synthetic RNA spike-in molecules as processing controls over a relevant dynamic range. When comparing blood collection tubes, serum mRNA seems very similar to EDTA plasma mRNA, but serum-derived small RNAs are markedly different in biotype composition compared to their plasma counterparts. Furthermore, several plasma tubes with preservation reagents do not stabilize RNA very well, as is reflected by increasing RNA concentrations and number of detected genes over time. Also, their reproducibility is generally compromised. In addition, we demonstrate large differences in RNA purification kit performance in terms of reproducibility, sensitivity, and observed transcriptome complexity. Among others, we note a 50-fold difference in mRNA yield and a 5-fold difference in the number of detected mRNAs. We summarized the results in 12 performance parameters that enable an informed selection of the most optimal sample processing workflow. In conclusion, using a systematic approach, we put forward robust quality control metrics for exRNA quantification methods with validated SOPs for sample collection, processing, and profiling. Our results are crucially important for all future RNA-based liquid biopsy-guided precision oncology applications. Authors in random order; abstract submitted on behalf of the exRNAQC Consortium.

Citation Format: Anneleen Decock, Jasper Anckaert, Celine Everaert, Justine Nuytens, Scott Kuersten, An Hendrix, Jo Vandesompele, Pieter Mestdagh, Bert Dhondt, Ruben Van Paemel, Kimberly Verniers, Gary Schroth, Carolina Fierro, Nurten Yigit, Kathleen Schoofs, Annelien Morlion, Jill Deleu, Eva Hulstaert, Francisco Avila Cobos, Nele Nijs, Eveline Vanden Eynde, Hetty Hilde Helsmoortel, Olivier De Wever, Annouck Philippron. Substantial performance differences among RNA purification kits and blood collection tubes in the Extracellular RNA Quality Control study—important considerations for liquid biopsies [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr B49.