Circulating plasma DNA is being increasingly used for biomedical and clinical research as a substrate for genetic testing. However, cell lysis can occur hours after venipuncture when using standard tubes for blood collection, leading to an increase in contaminating cellular DNA that may hinder analysis of circulating plasma DNA. Cell stabilization agents can prevent cellular lysis for several days, reducing the need for immediate plasma preparation after venipuncture, thereby facilitating the ease of blood collection and sample preparation for clinical research. However, the majority of cell stabilizing reagents have not been formally tested for their ability to preserve circulating plasma tumor DNA.

In this study, we compared the properties of two cell stabilizing reagents, the cell-free DNA BCT tube and the PAXgene tube, by collecting blood samples from metastatic breast cancer patients and measuring genome equivalents of plasma DNA by droplet digital PCR. We compared wild type PIK3CA genome equivalents and also assayed for two PIK3CA hotspot mutations, E545K and H1047R.

Our results demonstrate that blood stored for 7 days in BCT tubes did not show evidence of cell lysis, whereas PAXgene tubes showed an order of magnitude increase in genome equivalents, indicative of considerable cellular lysis.

We conclude that BCT tubes can prevent lysis and cellular release of genomic DNA of blood samples from cancer patients when stored at room temperature, and could therefore be of benefit for blood specimen collections in clinical trials.