RNA Integrity Number (RIN) detection is the gold-standard analytical approach for quantitatively assessing RNA quality prior to downstream molecular experiments such as RNA sequencing, microarray profiling, and quantitative RT-PCR. By assigning a numerical value from 1 to 10 based on the entire electrophoretic profile of an RNA sample, RIN detection provides objective, reproducible, and standardized quality control that safeguards the reliability of gene expression data.
Technical Overview
The RNA Integrity Number (RIN) is a computational quality metric introduced by Agilent Technologies that quantitatively evaluates the integrity of total RNA samples on a scale from 1 to 10, where a value of 10 represents completely intact RNA and a value of 1 represents highly degraded RNA. Prior to the development of the RIN algorithm, researchers relied heavily on the 28S to 18S ribosomal RNA ratio, with a ratio of approximately 2.0 traditionally considered indicative of intact eukaryotic RNA. However, this approach was subjective, prone to operator variability, and ignored much of the electrophoretic information contained in a sample profile.
The RIN algorithm overcomes these limitations by analyzing the complete electrophoretic trace obtained through microfluidic capillary electrophoresis. The algorithm extracts multiple features from the signal, including the heights of the 18S and 28S rRNA peaks, the fast-migrating region, the inter-peak region, and the baseline signal in degraded regions below the ribosomal peaks. These features are processed through a trained neural network model that produces a single, reproducible numerical score. Because the entire trace is considered, RIN is far more robust than simple peak-ratio assessments and enables consistent quality comparison across laboratories, instruments, and time points.
Numerical RNA integrity detection is essential because RNA is chemically unstable and highly susceptible to degradation by ubiquitous ribonucleases. Degraded RNA can introduce systematic bias into gene expression measurements, reduce library preparation efficiency, and generate misleading biological conclusions. Consequently, most sequencing facilities, core laboratories, and journals require documented RIN values as part of standard quality control documentation before accepting RNA samples for analysis.
Testing Samples
Total RNA from Cultured Cells
RNA extracted from mammalian or microbial cell cultures is among the most commonly tested sample types. Because cell culture conditions and harvest timing can be tightly controlled, these samples typically yield high RIN values of 8 or above when processed rapidly with RNase-free technique and immediate stabilization in lysis reagent or TRIzol.
Total RNA from Animal Tissues
Fresh, frozen, or preserved animal tissues including liver, brain, kidney, heart, and tumor specimens are routinely submitted for RIN analysis. Tissue RNA quality depends heavily on post-excision handling; samples flash-frozen in liquid nitrogen or preserved in RNAlater generally maintain excellent integrity, whereas tissues subjected to prolonged thaw cycles often show depressed RIN values.
Total RNA from Plant Tissues
Plant RNA presents unique challenges due to secondary metabolites, polyphenols, and polysaccharides that can co-purify with RNA and interfere with electrophoretic analysis. Specialized extraction protocols using CTAB or commercial plant RNA kits are employed before RIN assessment. Chloroplast rRNA species may introduce additional peaks that must be interpreted correctly.
Blood and Clinical Specimens
Whole blood, plasma, serum, and buffy coat-derived RNA are frequently evaluated, particularly in clinical research and liquid biopsy applications. Peripheral blood RNA is prone to rapid ex vivo gene expression changes and degradation, making stabilization in PAXgene or Tempus tubes at collection critical for preserving integrity.
FFPE Tissue RNA
RNA recovered from formalin-fixed paraffin-embedded (FFPE) tissue blocks is inherently fragmented due to crosslinking and chemical modification during fixation. Such samples rarely achieve RIN values above 3, so the field has adopted DV200, the percentage of RNA fragments longer than 200 nucleotides, as a complementary or alternative quality metric for these specimens.
Isolated RNA Fractions and Low-Input Samples
mRNA-enriched fractions, depleted rRNA preparations, small RNA isolates, and single-cell or low-input RNA samples can also be evaluated using high-sensitivity kits such as the RNA 6000 Pico assay, which detects picogram-level RNA concentrations and provides RIN or RIN-equivalent values when applicable.
Testing Items
Professional RNA integrity numerical detection services typically report the following parameters for each submitted sample:
- RNA Integrity Number (RIN): the primary numerical integrity score ranging from 1 to 10.
- RIN equivalent (RINe): the analogous metric generated by the Agilent TapeStation platform.
- RNA concentration: quantified from fluorescence signal area, typically reported in ng/µL.
- 28S/18S ratio: the classical ribosomal RNA peak ratio retained for reference and comparative purposes.
- DV200: percentage of RNA fragments exceeding 200 nucleotides, essential for FFPE-derived samples.
- Electropherogram trace: the full electrophoretic profile showing marker peaks, rRNA peaks, and degradation baseline.
- Gel-like virtual image: a simulated agarose gel representation generated from the digital trace.
- Quality flags and annotations: identification of genomic DNA contamination, marker anomalies, or out-of-range concentrations.
Testing Methods
Microfluidic Capillary Electrophoresis (Agilent Bioanalyzer)
The Agilent 2100 Bioanalyzer remains the reference platform for RIN determination. Total RNA samples are diluted to the appropriate concentration range, mixed with a fluorescent intercalating dye, and loaded onto a microfabricated chip alongside a size ladder and internal markers. The instrument performs automated electrophoretic separation through microchannels, detects fluorescent signal with a laser, and translates the signal into a digital electropherogram. Expert software then applies the RIN algorithm to generate the integrity score. The RNA 6000 Nano kit accommodates 25 to 500 ng/µL total RNA, while the RNA 6000 Pico kit extends sensitivity down to 50 to 5,000 pg/µL.
ScreenTape Electrophoresis (Agilent TapeStation)
The Agilent TapeStation system uses pre-packaged ScreenTape devices containing ready-to-use separation matrices and electrodes. This format minimizes chip preparation time and sample handling, making it well suited for high-throughput workflows. The system reports RINe values that correlate closely with traditional RIN but are derived from a slightly different feature-extraction algorithm. Sample volumes of only 1 µL are required, which is advantageous when material is limited.
Parallel Capillary Electrophoresis (Fragment Analyzer)
The Advanced Analytical Fragment Analyzer and its equivalent platforms perform automated capillary electrophoresis across 12 to 96 capillaries simultaneously using the Standard Sensitivity or High Sensitivity RNA kits. The system reports RQN, an RNA Quality Number analogous to RIN, and provides exceptional throughput for core facilities processing large sample cohorts.
Denaturing Agarose Gel Electrophoresis
For laboratories lacking microfluidic instrumentation, formaldehyde- or glyoxal-denaturing agarose gels with ethidium bromide or SYBR-safe staining offer a semi-quantitative alternative. Intact eukaryotic RNA displays sharp 28S and 18S bands at an approximate 2:1 intensity ratio with minimal smearing. This method is qualitative, operator-dependent, and consumes substantially more sample, so it is generally reserved for preliminary assessment or verification.
Quality Control Workflow
A complete detection workflow encompasses concentration measurement by fluorometric assay (Qubit or RiboGreen), purity assessment by UV spectrophotometry with A260/A280 and A260/A230 ratios, followed by integrity evaluation on a microfluidic or capillary electrophoresis platform. Only when all three dimensions of quality are acceptable should a sample proceed to downstream library construction or expression analysis.
Applications
RNA integrity numerical detection is applied across a broad spectrum of research, clinical, and industrial contexts:
- RNA-sequencing library preparation: most facilities require RIN values of 7.0 or higher for standard poly(A)-selected workflows, since degraded input causes pronounced 3-prime bias and reduced library complexity.
- Microarray expression profiling: hybridization-based platforms typically demand RIN values of 8.0 or above to ensure robust and comparable signal intensities.
- Quantitative RT-PCR and digital PCR: primer design across exon junctions and amplicon length selection are guided by RNA quality scores, with short amplicons recommended for moderately degraded samples.
- Clinical diagnostics and pathology: integrity scoring supports qualification of biopsy and FFPE specimens for molecular testing panels in oncology and infectious disease.
- Biobanking and sample repository management: routine RIN auditing verifies that long-term storage conditions at minus 80 degrees Celsius preserve specimen utility.
- Drug development and toxicogenomics: regulatory submissions frequently include documented RNA quality metrics supporting transcriptomic safety data.
- Single-cell and spatial transcriptomics: although these methods tolerate some degradation, input quality scoring remains critical for protocol optimization and reproducibility.
FAQ
What RIN value is considered acceptable?
Acceptance thresholds depend on the downstream application. RIN values of 8 to 10 are considered excellent and suitable for any application including microarrays. Values of 7 to 8 are generally acceptable for RNA-seq. Samples between 5 and 7 may still be usable for qPCR with short amplicons or 3-prime RNA-seq protocols, while samples below 5 are usually unsuitable for full-length transcriptome analysis without specialized degraded-RNA kits.
Why did my sample receive a low RIN despite high concentration?
Concentration and integrity are independent properties. Common causes of low RIN include ribonuclease contamination during extraction, delayed tissue stabilization, repeated freeze-thaw cycles, aqueous storage at inappropriate temperatures, or residual chemicals that fluoresce and distort the electropherogram baseline.
Can degraded RNA still be used for sequencing?
Yes, within limits. When RIN falls below 7, protocols based on random priming, rRNA depletion rather than poly(A) selection, or targeted capture are preferred. For severely fragmented FFPE RNA, the DV200 metric is a better predictor of library success, with DV200 above 50 percent generally supporting reliable whole-transcriptome library construction.
How much RNA is required for RIN detection?
The Bioanalyzer RNA 6000 Nano assay requires approximately 1 µL of sample at 25 to 500 ng/µL, whereas the Pico assay accepts concentrations as low as 50 pg/µL. The TapeStation requires only 1 µL at 5 to 100 ng/µL with its High Sensitivity assay, making it suitable for scarce clinical material.
How should samples be stored and shipped for integrity testing?
Purified RNA should be stored at minus 80 degrees Celsius in RNase-free water or low-concentration EDTA buffer, aliquoted to avoid repeated freeze-thaw cycles, and shipped on dry ice. Tissues should be flash-frozen in liquid nitrogen or stabilized in RNAlater before shipment on dry ice with temperature monitoring.
Is RIN applicable to prokaryotic RNA?
The standard RIN algorithm was trained on eukaryotic traces and does not directly apply to prokaryotes, whose 23S and 16S rRNA peaks differ in size and ratio. Bacterial RNA quality is typically evaluated qualitatively from the electropherogram, the 23S/16S ratio, and the extent of low-molecular-weight smearing, although platform-specific prokaryotic metrics continue to be developed.