RNA Quality and Integrity Testing: Comprehensive Assessment Services and Technical Guide

RNA quality and integrity testing is an essential quality control step that determines whether RNA samples are suitable for demanding downstream applications such as RNA sequencing, microarray analysis, and RT-qPCR. By evaluating key parameters including concentration, purity ratios, and the RNA Integrity Number (RIN), laboratories can prevent failed experiments, reduce sequencing bias, and ensure reproducible results. This guide provides a comprehensive overview of RNA integrity assessment, covering sample types, testing parameters, analytical methods, and expert answers to frequently asked questions.

Technical Overview

RNA quality and integrity testing refers to the systematic evaluation of RNA samples to determine their concentration, purity, and structural intactness prior to downstream molecular analysis. Because RNA is highly susceptible to degradation by ubiquitous ribonucleases (RNases), even minor lapses in sample handling can compromise experimental outcomes. Degraded RNA leads to biased gene expression profiles, reduced library complexity, inaccurate quantification, and irreproducible results, making rigorous quality assessment indispensable.

A complete RNA quality evaluation typically encompasses three dimensions: quantification (how much RNA is present), purity (whether contaminants such as proteins, phenol, salts, or genomic DNA are present), and integrity (how intact the RNA molecules remain). Integrity is most commonly expressed as the RNA Integrity Number (RIN), an algorithm-derived value ranging from 1 (completely degraded) to 10 (fully intact), developed by Agilent Technologies. Traditionally, the 28S to 18S ribosomal RNA ratio was used as an integrity indicator, with a value near 2.0 considered indicative of intact eukaryotic total RNA, although RIN has largely superseded this approach due to its objectivity and reproducibility.

For severely degraded samples, such as those extracted from formalin-fixed paraffin-embedded (FFPE) tissues, the DV200 metric—the percentage of RNA fragments longer than 200 nucleotides—is recommended instead of RIN, as it more accurately predicts library construction success from fragmented material. A professional testing service applies the appropriate metric to each sample type and delivers standardized reports that support informed experimental decisions.

Testing Samples

RNA quality and integrity testing services accommodate a wide range of biological materials and purified RNA preparations. Proper sample collection, stabilization, and storage are critical pre-analytical factors that directly influence test results.

Animal Tissues

Fresh or flash-frozen animal tissues from mammals, rodents, fish, and other organisms can be submitted for analysis. Tissues should be excised rapidly, rinsed to remove blood contamination, snap-frozen in liquid nitrogen, and stored at -80°C to minimize RNase activity. RNAlater stabilization reagent is an acceptable alternative when flash-freezing is not feasible. Commonly tested tissues include liver, brain, heart, kidney, spleen, lung, and tumor specimens.

Plant Tissues

Plant materials such as leaves, roots, stems, seeds, and fruits present unique challenges due to polysaccharides, polyphenols, and secondary metabolites that co-purify with RNA and interfere with spectrophotometric readings. Specialized extraction protocols and additional purification steps may be required before integrity assessment can yield reliable results.

Cultured Cells

Mammalian cell lines, primary cells, stem cells, and microbial cultures can be submitted as cell pellets. Cells should be harvested gently, washed with phosphate-buffered saline, pelleted by centrifugation, and either frozen immediately or lysed directly in a denaturing reagent to inactivate RNases.

Blood and Body Fluids

Whole blood collected in EDTA tubes, peripheral blood mononuclear cells (PBMCs), serum, and plasma are accepted, with particular attention to globin mRNA interference in whole blood preparations. For circulating RNA and extracellular vesicle studies, RNase-free plasma processing protocols are applied.

FFPE Tissue Samples

Archival formalin-fixed paraffin-embedded blocks and sections are routinely evaluated, typically using the DV200 metric rather than RIN due to the inherently fragmented nature of FFPE-derived RNA. Fixation duration and conditions strongly influence RNA preservation quality.

Purified RNA Preparations

Previously isolated total RNA, messenger RNA (mRNA), long non-coding RNA (lncRNA), small RNA, and microRNA (miRNA) fractions can be submitted directly for concentration determination, purity analysis, and integrity profiling, provided samples are transported on dry ice in RNase-free conditions.

Testing Items

A standard RNA quality assessment report includes the following core parameters, each of which addresses a distinct aspect of sample suitability:

• RNA Concentration: The absolute quantity of RNA, measured in ng/µL, determined by fluorometric assays (Qubit RNA HS Assay) or spectrophotometry, enabling accurate input normalization for downstream reactions.
• Purity – A260/A280 Ratio: An absorbance ratio used to detect protein and phenol contamination. Pure RNA typically yields a ratio of approximately 2.0; values significantly below 1.8 suggest protein, phenol, or other contaminants that absorb near 280 nm.
• Purity – A260/A230 Ratio: A second purity indicator sensitive to guanidine salts, phenol, carbohydrates, and EDTA. Acceptable values generally fall between 2.0 and 2.2; lower ratios indicate carryover from extraction reagents that may inhibit enzymatic reactions.
• RNA Integrity Number (RIN): A digital score from 1 to 10 generated from electrophoretic profiles by the Agilent 2100 Bioanalyzer or TapeStation systems, objectively reflecting the degree of degradation across the entire RNA population.
• 28S/18S rRNA Ratio: A classical integrity metric obtained from gel electrophoresis or electrophoretic traces, with a ratio of approximately 1.5 to 2.0 indicating intact eukaryotic RNA.
• DV200 Value: The percentage of RNA fragments exceeding 200 nucleotides, recommended by Illumina for FFPE samples, where DV200 values above 50% generally support successful library preparation with appropriate protocols.
• Small RNA Content: Optional profiling of miRNA and small RNA fractions, which is relevant for microRNA sequencing projects since small RNAs can be retained even when long RNA species are degraded.

Testing Methods

Multiple complementary platforms are employed depending on sample quantity, degradation status, and the required resolution of the analysis. Combining methods provides the most complete picture of RNA quality.

Agilent 2100 Bioanalyzer Analysis

The Agilent 2100 Bioanalyzer is the industry gold standard for RNA integrity assessment. Using microfluidic capillary electrophoresis with RNA 6000 Nano or Pico LabChips, the system separates RNA fragments by size, generates electropherograms, and algorithmically computes the RIN value. The Nano chip covers a broad concentration range (25–500 ng/µL total RNA), while the Pico chip enables analysis of trace samples down to 50–5,000 pg/µL. The resulting electropherogram displays distinct 18S and 28S rRNA peaks for intact samples, with degradation appearing as a shift of the trace toward smaller fragments and an elevated baseline in the fast-migrating region.

Agilent TapeStation Analysis

The TapeStation platform uses screen tape technology to deliver rapid, high-throughput RNA quality screening with minimal sample input (1–2 µL). It reports the RNA Quality Number (RQN), a metric analogous to RIN, and supports convenient genomic screening workflows in genomics core facilities.

Denaturing Agarose Gel Electrophoresis

Traditional formaldehyde-denaturing agarose gel electrophoresis remains a cost-effective method for visualizing RNA integrity. Intact total RNA displays sharp, clearly defined 28S and 18S rRNA bands with an approximate 2:1 intensity ratio, whereas degraded RNA appears as smeared, low-molecular-weight fragments. This method requires relatively large sample quantities and provides only semi-quantitative assessment compared with capillary electrophoresis.

UV Spectrophotometry

NanoDrop or equivalent microvolume spectrophotometers measure absorbance at 260 nm for concentration estimation and generate full absorbance spectra (220–350 nm) for purity evaluation through the A260/A280 and A260/A230 ratios. Although rapid and sample-sparing, spectrophotometry cannot distinguish RNA from free nucleotides or DNA and cannot assess integrity.

Fluorometric Quantification

Qubit or RiboGreen fluorescence-based assays use RNA-binding dyes to provide highly specific and accurate quantification, even at picogram levels, and are less affected by contaminants than absorbance methods. Fluorometric values are recommended for calculating precise library input amounts.

Applications

RNA quality and integrity testing is a prerequisite for a broad spectrum of molecular biology and genomics applications:

• RNA Sequencing (RNA-seq): Verifying that RIN and concentration thresholds are met before library construction, preventing 3′ coverage bias and distorted expression measurements caused by degraded input.
• Small RNA and miRNA Sequencing: Confirming the preservation of small RNA fractions and excluding preparations dominated by degradation artifacts.
• Microarray Gene Expression Profiling: Ensuring labeled cDNA or cRNA targets hybridize uniformly, as most array platforms require high-quality input for valid comparisons.
• RT-qPCR and RT-PCR: Screening RNA prior to reverse transcription, since degradation preferentially affects amplicons targeting the 5′ regions of transcripts and invalidates reference gene normalization.
• Single-Cell and Low-Input Transcriptomics: Assessing trace RNA samples with high-sensitivity electrophoretic platforms before committing material to expensive workflows.
• cDNA Library Construction and Full-Length Cloning: Confirming intactness essential for obtaining complete coding sequences and full-length transcripts.
• Northern Blotting and RACE: Guaranteeing that hybridization signals and transcript length determinations reflect true biology rather than degradation artifacts.
• Biobanking and Clinical Research: Documenting the quality of archived specimens and qualifying FFPE samples for retrospective transcriptomic studies.

FAQ

What RIN value is required for RNA sequencing?

For standard bulk RNA-seq, a RIN of 7 or above is generally recommended, with RIN ≥ 8 considered ideal. Samples with RIN between 5 and 7 can often be processed using degradation-tolerant protocols, while heavily degraded samples (RIN < 3 or DV200 < 30%) require specialized FFPE-oriented kits and are best suited to 3′-end counting workflows.

How should RNA samples be stored and shipped?

Purified RNA should be stored at -80°C in RNase-free water or low-concentration EDTA buffer to chelate divalent cations that catalyze hydrolysis. Samples must be shipped on dry ice with sufficient coolant for at least 48 hours of transit. Repeated freeze-thaw cycles should be strictly avoided, and aliquoting is strongly recommended.

What causes a low A260/A230 ratio and how can it be corrected?

Low A260/A230 values typically result from carryover of guanidinium thiocyanate, phenol, ethanol, or salts from column-based or TRIzol extraction procedures. Remedies include additional column wash steps, thorough drying before elution, or a secondary cleanup using a silica spin column or lithium chloride precipitation.

Can partially degraded RNA still be used?

Yes, depending on the application. qPCR assays targeting short amplicons (60–120 bp) tolerate moderate degradation well. RNA-seq can accommodate degraded input with appropriate library kits, provided DV200 is documented. In contrast, full-length cDNA synthesis, Northern blotting, and long-read sequencing require high-integrity RNA.

Why do my RIN and gel results disagree?

Discrepancies arise because RIN evaluates the entire electrophoretic profile computationally, whereas gel assessment relies on visual inspection of rRNA bands, which can be affected by loading amount, staining, and non-denaturing conditions. Capillary electrophoresis results under denaturing conditions are considered more objective and reproducible.

How much RNA is required for a quality test?

Agilent Bioanalyzer RNA 6000 Nano chips require only 1 µL at 25–500 ng/µL, while Pico chips handle trace samples from 50 pg/µL upward. Qubit quantification consumes 1–10 µL depending on concentration. Sample-sparing microfluidic platforms make comprehensive testing feasible even for limited or precious specimens.