Quality Control Checkpoints in RNA Sample Prep: Beyond A260/A280

Team Dynamic Matrices | 22 February 2026

For decades the RNA quality gate has been one number: absorbance at 260 nm divided by absorbance at 280 nm, hoping for something near 2.0. That ratio tells you whether protein or phenol is present. It tells you nothing about integrity, genomic DNA, ribosomal RNA load or polymerase inhibitors. A sample can pass A260/A280 cleanly and fail in RT-qPCR, RNA-seq or long-read sequencing. When it fails there, it has already consumed days and hundreds of euros. Here is the layered QC system we use instead.

What A260/A280 misses

Degradation. Fragmented and intact RNA absorb identically at 260 nm. A degraded sample can have a perfect ratio. Integrity needs capillary electrophoresis: RIN (Agilent) or RQN (other platforms) on a 1 to 10 scale, and for FFPE the DV200 fraction (Schroeder et al., BMC Molecular Biology, 2006).

Genomic DNA. DNA absorbs at 260 nm like RNA and barely moves the ratio at contamination levels that produce false-positive RT-qPCR signals and intronic reads in RNA-seq. The only reliable detection is a qPCR reaction with no reverse transcriptase, targeting a genomic region.

Concentration. UV absorbance counts free nucleotides, salt, phenol and gDNA as RNA. Overestimates of two to three-fold are common in low-input preps, and they lead directly to under-loaded libraries. Fluorometry with an RNA-specific dye (RiboGreen, Qubit RNA HS) is far more accurate and is the input basis every library kit assumes.

rRNA load. Ribosomal RNA is 80 to 90 percent of total RNA and is invisible to absorbance. If depletion or enrichment underperformed, most of your reads go to rRNA and you find out after sequencing.

The four checkpoints

Checkpoint 1: Immediately after extraction

• Fluorometric concentration
• A260/A280 and A260/A230 for gross contamination
• No-RT qPCR for gDNA on a genomic target (intron or intergenic)

This is the cheapest point to catch a problem. A gDNA-positive sample gets DNase treatment and re-check; a low-A260/A230 sample gets re-purified.

Checkpoint 2: Integrity

RIN or RQN by capillary electrophoresis on representative samples at minimum, and on every irreplaceable sample without exception. For FFPE use DV200; for EV or small RNA preps use a small-RNA assay; for bacterial RNA use the prokaryotic algorithm. Thresholds:

This checkpoint is the one that most often explains a downstream failure retroactively. Do it prospectively instead.

Checkpoint 3: Enrichment or depletion efficiency

Before committing full sequencing depth, confirm that rRNA depletion or target enrichment worked. A two-primer qPCR (18S or 28S versus a housekeeping mRNA, before and after depletion) takes an hour and gives a depletion percentage. If your chemistry routinely leaves 5 to 20 percent rRNA, you will see it here rather than in the sequencing report.

This is also where chemistry choice shows. Probe-based and RNase H depletion lose efficiency on fragmented and low-input RNA; sequence-selective phase-separation capture holds efficiency across those ranges (we reach over 98 percent depletion with riboLASSO in our benchmarks, including on degraded input). Better chemistry reduces the mitigation you need downstream, but it does not replace this check.

Checkpoint 4: Library QC

Fragment size distribution and adapter-dimer content by capillary electrophoresis, plus library concentration by qPCR (KAPA or equivalent). This confirms everything upstream produced a usable library and sets loading concentration.

What it costs and what it saves

Checkpoints 1 to 3 add roughly 90 minutes and a few euros per sample. A failed library costs a kit, a lane share, and a week. The arithmetic is not close.