Norgen's cf-DNA/cf-RNA Preservative Tubes are closed, evacuated plastic tubes for the collection and the preservation of cf-DNA, circulating tumor DNA, cf-RNA and circulating tumor cells in human whole blood samples during storage and shipping. Using these tubes in combination with Norgen's Plasma/Serum Cell-Free Circulating DNA Purification Kits or Norgen's Plasma/Serum RNA Purification Kits enables the purification and concentration of an inhibitor-free cf-DNA/ct-DNA/cf-RNA in a very small elution volume. Plasma recovered from Norgen's cf-DNA/cf-RNA Preservative Tubes is also compatible with any other cf-DNA and/or cf-RNA purification method. The purified cf-DNA, ct-DNA and cf-RNA are compatible with any downstream application assays, including PCR, qPCR, rt-qPCR, methylation-sensitive PCR, Southern Blot analysis, gene expression analysis, microarrays and NGS.