For extracting plasma cell-free DNA using the magnetic bead method, are there any kits recommended that can remove heparin inhibition?

For liquid biopsy cfDNA, if qPCR shows inhibition, don't rush to replace the entire extraction kit. First confirm whether the inhibition is caused by heparin or elution buffer carryover. If it's heparin inhibition, when choosing a magnetic bead method, prioritize whether the instructions explicitly state "heparin-tolerant/heparin removal," or include heparinase or a high-salt wash step. Some domestic cfDNA magnetic bead kits additionally include heparinase digestion or optimized binding buffer to reduce heparin co-extraction. For compatibility with both manual and automated workflows, choose an open-system magnetic bead method. Magnetic bead sedimentation time should ideally be within 1 minute, and elution volume should be adjustable to 30–80 μL. It is recommended to first request a 50-test trial pack, spike plasma with heparin, and perform recovery and qPCR internal standard comparison—don't just look at yield. In terms of cost, domestic OEM per-test pricing is typically in the tens of RMB; inquire for specific pricing based on packaging and payment terms. For lead time, domestic in-stock items are generally 3–5 days.

If you already have an automated extraction instrument, first ask the instrument manufacturer whether it has a compatible open magnetic bead-based cfDNA protocol. For magnetic bead kits, check the particle size and magnetic response, as not all magnetic beads are compatible. For manual and automated compatibility, the elution volume and shaking frequency usually need to be adjustable. When using 1–2 mL plasma, some plates do not have a sufficient maximum loading volume, so pretreatment concentration or a deep-well plate option is required. For heparin inhibition, do not repeatedly freeze-thaw plasma before extraction, as heparin becomes more difficult to remove after binding to DNA. For validation, known positive cfDNA standards or fragmented DNA spiked into heparin-containing plasma can be used to compare recovery; for qPCR internal controls, mitochondrial or single-copy genes can be used, and do not rely only on concentration. For small packaging, it is recommended to request 50 tests directly rather than buying a large box first, and switch only after three batches show stable repeatability. When comparing suppliers, check whether they can provide third-party data or real users, and do not just listen to claims that they “can remove heparin.”

Many domestic manufacturers of cfDNA magnetic beads are willing to provide 50-test small packages for trials. Contact the regional sales representative directly and ask clearly whether they have a "heparin removal version" and a "manual/automated universal" protocol. For per-test cost, do not focus only on the kit list price; include magnetic rod sleeves, elution tubes, and quality control materials. If sample volume is stable, you can negotiate annual pricing or bulk packaging, which is usually considerably lower per test than the 50-test pack. For lead time, domestic in-stock items are generally within one week, while imported aliquoted products depend on customs clearance and often take 2-4 weeks, so it is not advisable to wait if urgent. During validation, it is recommended to split the same plasma into two portions, one with heparin added and one without, extract them separately, and compare qPCR Ct differences. Also run an extraction blank to determine whether it is heparin inhibition or elution inhibition. If qPCR inhibition is still obvious, you can pass the extract through a silica column or treat it with heparinase, but this will lose a small amount of cfDNA and is not suitable for low-abundance loci.

Heparin strongly inhibits subsequent qPCR. We have tried adding heparinase treatment, but the recovery rate decreases.

Same here. After plasma cfDNA extraction, the sequencing library concentration is always low, and we suspect heparin contamination.