Zubair Khalid

Virologist/Molecular Biologist | Veterinarian | Bioinformatician

Conventional & Molecular Virology • Vaccine Development • Computational Biology

Dr. Zubair Khalid is a veterinarian and virologist specializing in conventional and molecular virology, vaccine development, and computational biology. Dedicated to advancing animal health through innovative research and multi-omics approaches.

Dr. Zubair Khalid - Veterinarian, Virologist, and Vaccine Development Researcher specializing in Computational Biology, Multi-omics, Animal Health, and Infectious Disease Research

Blog · Guides · Published 2026-07-12

RNA Extraction Quality Control: What Purity and Integrity Measures Mean

RNA extraction quality control (QC) is the set of checks and measurements that tell you whether your RNA is fit for downstream analysis. You should use this guide if you are planning to extract RNA for any sequencing or qPCR experiment, especially if you will submit samples for RNA-seq, single-cell RNA-seq, or small RNA profiling. The goal is to help you interpret spectrophotometer readings, bioanalyzer traces, and gel images so you can confidently decide whether to proceed with library preparation or repeat the extraction.

At a Glance

QC Parameter Ideal Range Common Method What It Indicates
Yield Depends on sample type (e.g., 1,10 µg from 10^6 cells) Fluorometry (Qubit) Amount of RNA recovered
A260/A280 1.8 , 2.1 NanoDrop Protein or phenol contamination
A260/A230 1.8 , 2.2 NanoDrop Guanidine salt or carbohydrate contamination
RIN / RQN ≥7 (ideal ≥8) for most RNA-seq Bioanalyzer / Fragment Analyzer Full length integrity of rRNA
DV200 >70% if using degraded samples Bioanalyzer Percentage of fragments >200 nt

The table above summarizes the metrics you will encounter. Below we unpack what each metric means in practice and how to use them to decide on sample suitability.

Sample Handling and Yield

Sample handling begins before extraction. Freezing and thawing protocols dramatically affect RNA quality. For example, a 2024 study on human milk samples showed that immediate freezing at −80°C followed by extraction within 30 days preserved RNA integrity better than storage at −20°C preserving RNA quality when freezing. For blood samples, the choice of lysis method matters. A comparison of TRIzol, Invitrogen, and Qiagen systems for whole blood found that RBC lysis before extraction reduced hemoglobin contamination and improved both purity and yield comparison of RNA extraction.

Yield is the total amount of RNA you recover. It is best measured with a fluorometric assay (like Qubit) because UV absorbance overestimates RNA in the presence of contaminants. Yield depends on sample type, tissue weight, and extraction efficiency. If your yield is lower than expected, check your homogenization protocol or consider adding carrier RNA for low‑input samples such as serum optimization of miRNA serum extraction.

Purity Measures: A260/A280 and A260/A230

Purity is assessed by comparing absorbance at different wavelengths. The A260/A280 ratio indicates contamination by proteins or phenol. Pure RNA gives a ratio between 1.8 and 2.1. A lower ratio suggests protein carryover, a higher ratio may indicate degraded RNA or residual phenol. The A260/A230 ratio detects guanidine salts (commonly from TRIzol) and carbohydrates. Good RNA has a ratio above 1.8. If A260/A230 is low, an extra ethanol wash or a column‑based cleanup can help.

For example, when extracting RNA from liver and visceral adipose tissue for single‑nucleus RNA‑seq, the authors of a 2024 protocol emphasized that A260/A230 values below 1.5 led to poor reverse transcription efficiency and had to be re-extracted protocol for minimized‑bias profiling. Always record these ratios and note any color or cloudiness in the sample, which indicate contamination.

Integrity Measures: RIN, RQN, and DV200

Integrity measures how intact the RNA molecules are. The most common metric is the RNA Integrity Number (RIN), calculated by Agilent Bioanalyzer software from the ratio of 28S to 18S ribosomal RNA peaks. An RIN of 10 is perfectly intact, while RIN 1 is completely degraded. For most bulk RNA‑seq applications, RIN ≥7 is acceptable, but many journals and core facilities require RIN ≥8.

For samples that are inherently degraded, such as formalin‑fixed paraffin‑embedded (FFPE) tissue, the DV200 metric is more useful. DV200 reports the percentage of RNA fragments longer than 200 nucleotides. The EMBL‑EBI training materials on RNA‑seq QC recommend DV200 >70% for standard library preparation and >50% for specialized protocols designed for degraded RNA EMBL‑EBI Training. If your sample has low RIN but adequate DV200, you can still proceed with certain library kits.

For small RNA studies, such as those examining blood‑based microRNAs as biomarkers of insulin resistance blood‑based microRNAs as biomarkers, the integrity of small RNAs is not always reflected by RIN. In those cases, check the small RNA region on the bioanalyzer trace separately.

Suitability for Downstream Methods

Different downstream applications have different tolerance thresholds. The table below summarizes decision criteria.

Downstream Method Minimum RIN Minimum DV200 Special Notes
Standard poly‑A RNA‑seq ≥7 (≥8 preferred) Not typically used Low RIN causes 3ʹ bias
Total RNA‑seq (rRNA‑depleted) ≥6 >70% Accepts some degraded RNA
Single‑cell RNA‑seq (scRNA‑seq) Not applicable for poly‑A >70% Quality assessed per cell
Small RNA sequencing Not required Check small RNA peak Use size‑selection step
Quantitative PCR (qPCR) ≥5 >50% Can tolerate moderate degradation

For single‑cell RNA‑seq, the key QC step happens after sequencing, when you filter cells by mitochondrial content and gene counts Single‑Cell RNA‑seq Quality Control. However, poor input RNA quality will increase the proportion of low‑quality cells. The Galaxy Training Network illustrates these concepts with practical workflows Galaxy Training Network.

Decision Criteria for Repeat

You should repeat the extraction if:

  • A260/A280 is below 1.7 or above 2.2 (after checking for phenol carryover).
  • A260/A230 is below 1.5 (cleanup may fix values between 1.5 and 1.8).
  • RIN is below 5 for standard RNA‑seq, or below 6 if you have ample material.
  • Yield is too low to proceed with your library protocol (check kit requirements).

If the sample is precious and cannot be re‑obtained, you may still proceed with modifications. For example, the NCBI Sequence Read Archive accepts runs from degraded RNA as long as it is documented NCBI Sequence Read Archive. Always include your QC metrics in the submission metadata. If you are analyzing blood samples with high globin mRNA content, consider using a globin depletion kit rather than repeating the extraction.

Practical Workflow for RNA Extraction QC

  1. Immediately after elution: Quantify by fluorometry (Qubit) and measure absorbance ratios (NanoDrop). Record the A260/A280 and A260/A230.
  2. Run 1 µL on a Bioanalyzer or Fragment Analyzer to obtain RIN or RQN. For FFPE or degraded samples, also record DV200.
  3. Check the electropherogram: Look for a flat baseline and distinct 28S and 18S peaks (in mammalian samples). A bump in the small RNA region indicates degradation.
  4. Compare results against the minimal thresholds for your intended downstream method (see table above).
  5. Make a pass/fail decision using the repeat criteria. If sample passes, store at −80°C in aliquots to avoid freeze‑thaw cycles.
  6. Document everything: Record the sample ID, extraction method, concentration, purity ratios, and integrity numbers. This metadata is required for publication and for submission to public repositories Bioconductor.

Common Mistakes

  • Relying solely on NanoDrop for concentration: NanoDrop overestimates RNA in the presence of free nucleotides or contaminants. Always cross‑check with Qubit.
  • Ignoring low A260/A230 values: Many researchers proceed because the A260/A280 looks good. Low A260/A230 indicates carryover of guanidine salts that can inhibit reverse transcriptase.
  • Freeze‑thawing RNA: RNA in water is stable at −80°C but degrades with each freeze‑thaw cycle. Aliquot before storage.
  • Using RIN as the only metric for degraded samples: For samples like serum or milk, DV200 is more informative.
  • Not running a gel or bioanalyzer for every sample: Some labs only check a subset. For critical experiments, especially those using valuable clinical samples, check every sample.
  • Forgetting to include a positive control: A known high‑quality RNA sample helps you distinguish batch effects from extraction problems.

Limits and Uncertainty

QC metrics are guidelines, not absolute rules. A sample with RIN 6 can still produce good libraries if the mRNA is not severely fragmented. Conversely, a sample with RIN 9 may have degraded mRNA if the 28S/18S ratio is driven by leftover rRNA.

The interpretation of A260/A280 varies by pH and buffer. In RNA stored in EDTA, the ratio may be artificially high. Always use the same dilution buffer for all measurements.

For single‑nucleus RNA‑seq, a protocol using integrated snRNA‑seq found that sample quality is better assessed by nucleus recovery and gene detection than by bulk RNA metrics protocol for minimized‑bias profiling. This means you may need to temper your rejection of moderate‑RIN samples.

When working with archival serum samples, extraction optimization shows that even modest yields can yield useful miRNA profiles optimization of miRNA serum extraction. The decision to repeat should factor in the biological question and available material.

Frequently Asked Questions

1. What is the difference between RIN and RQN? RIN (RNA Integrity Number) and RQN (RNA Quality Number) are equivalent metrics. RIN is used by Agilent Bioanalyzer, while RQN is used by Fragment Analyzer. Both range from 1 (totally degraded) to 10 (intact). Values are not perfectly interchangeable between platforms because the algorithms differ, but for practical purposes you can treat them similarly.

2. Can I use RNA with an A260/A280 above 2.1? A value above 2.1 can indicate RNA hydrolysis or contamination with phenol. First check the A260/A230. If that is also abnormal, consider a cleanup step or re‑extract. If both ratios are borderline but RIN is good and yield is sufficient, you can proceed but document the anomaly.

3. How should I store extracted RNA for long‑term use? Store RNA at −80°C in nuclease‑free water or TE buffer (pH 8.0). TE buffer is preferable because the EDTA chelates magnesium ions, reducing RNA degradation. Avoid freeze‑thaw cycles by making single‑use aliquots. Do not store RNA in liquid nitrogen unless absolutely necessary, as the rapid temperature change can cause condensation and ice crystal damage.

4. My RIN is 7.5 but the 28S/18S ratio is only 1.2. Is that a problem? A 28S/18S ratio of 1.2 (expected 2.0 for intact RNA) suggests some degradation even though the overall RIN is acceptable. This is common in samples with high RNase activity. For standard RNA‑seq, this is usually fine. For applications that require full‑length transcripts (e.g., isoform‑level analysis), you may want to re‑extract using a better RNase inhibitor.

References and Further Reading

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