For qPCR with low-input RNA, which reverse transcriptase brand is more reliable?

From a procurement and validation perspective, it is recommended to first have two distributors provide small-pack or trial-pack samples, preferably for comparison on the same batch of samples within the same week. Focus on two parameters: detection rate for low-copy genes and no-RT control signal. SuperScript IV has a 50-reaction small pack, and Vazyme HiScript III often has small RT packs without qPCR, with more flexible domestic stock availability and pricing. When asking vendors about lead time and price, clarify tax inclusion, cold-chain shipping, and lot number to avoid aliquoting after arrival affecting enzyme activity. During procurement, we require suppliers to provide trial packs from the same lot, and subsequent orders are supplied according to the trial lot number. For serum exosomal RNA, poor RIN is normal; internal controls and linear gradients can be used to determine whether the reverse transcriptase is suitable, without pursuing how low the absolute Ct value is.

For those who have done low-input exosomal RNA comparisons, the experience is not to look only at absolute Ct values, but to examine replicate wells and linearity for low-copy genes. It is recommended to split the same RNA into several tubes, reverse transcribe with SSIV and HiScript III separately, set up 3 technical replicates for qPCR, and calculate ΔCt and reference gene variation. SSIV has advantages for highly degraded RNA, but note that it is not cheap, with a small pack of 50 reactions; HiScript III has fast lead times for small packs, and you can ask a distributor to apply for a trial. If the lab has many subsequent samples, the cost advantage of HiScript III is obvious; but if samples are precious and batch-to-batch variation is large, the stability of SSIV may be more reassuring. The key is still to do a comparison first, and not trust only manufacturer data.

For low-input RNA reverse transcription, the enzyme is only one part of the workflow. SuperScript IV is indeed reliable in terms of thermostability and low-template affinity, but it is relatively expensive; among domestic options, HiScript III also performs well with low templates, and its kits often include a 5× gDNA wiper, making genomic DNA removal more convenient. It is advisable to first standardize the extraction method and DNase treatment conditions, then use the same batch of RNA at around ten-plus nanograms for serial dilutions (e.g., undiluted, 1:2, 1:4) to compare the Ct values and melting curves of the two kits. Fluctuating Ct values for low-copy genes are not necessarily due only to the reverse transcriptase; primer design and the qPCR system also matter. In our lab, for low-input samples, we place more emphasis on whether the no-reverse-transcriptase control is clean; after removing genomic contamination, Ct values can stabilize within 2–3 cycles.