Are there exosome RNA liquid biopsy kits suitable for small-volume serum?

Using 0.5-1 ml serum for exosomal RNA, low yield is a common issue. It is recommended to prioritize membrane affinity column/membrane adsorption kits, which are more friendly to low-volume samples than precipitation methods; precipitation methods have more contaminating proteins and RNA purity may be unstable. Sample processing before extraction is very important: serum should not undergo repeated freeze-thaw cycles; after centrifugation at 3000g, collect the supernatant and pass it through a 0.22 μm filter or centrifuge at 10000g to remove cell debris and platelets. During extraction, add exogenous cel-miR-39 as an internal standard, and subsequently use qPCR to correct for extraction efficiency. A Ct value above 30 is not necessarily all due to extraction problems; reverse transcription and primer efficiency should also be checked.

When working with both miRNA and lncRNA, it is essential to specifically ask whether the kit retains RNA larger than 200 nt. Many exosomal RNA kits are optimized only for small RNA, resulting in very low lncRNA recovery. It is recommended to aliquot the same batch of 0.5 ml serum and compare the total RNA yield, as well as miRNA and lncRNA recovery by Small RNA microarray or RT-qPCR, across two or three kits. With a budget under 200 yuan, imported exoRNeasy may exceed the limit; consider domestic membrane affinity column products, or negotiate a small-package trial price with the distributor. Keep the elution volume as low as possible, down to 10–20 μl; if the yield is still low, use a Pico chip or a low-input reverse transcription kit.

For early breast cancer marker screening with a small sample size, it is advisable not to aim to obtain all RNA in one go, but rather to optimize in steps. For reagents, you can contact domestic manufacturers of exosome products such as RiboBio, Umibio, and Echo Biotech to ask whether they have extraction kits specifically for small-volume serum and in-stock trial samples. In terms of experimental design, do not test too many genes simultaneously with 0.5 ml serum; it is better to split it into two tubes: one tube for miRNA first, and the other for enriching lncRNA, to avoid mutual dilution. If qPCR Ct values are high, you can try pre-amplification or switch to a reverse transcription system specifically designed for low-input RNA. With a budget of under 200 yuan, pay attention to whether the extraction kit includes internal standards and quality controls.

Tested 100 µL serum with a certain brand; RNA yield was low but qPCR peaks were detectable. A miRNA panel is recommended.

For small-volume sample extraction, carrier RNA must be added; otherwise, there will be significant loss.