Methods for preserving and processing cell-free nucleic acids are disclosed. The method includes a blood collection tube including a composition formulated for stabilizing cell-free nucleic acids within a blood sample. The composition includes least one formaldehyde releaser preservative agent; ethylenediaminetetraacetic acid (EDTA); and one or more solvents; and at least some formaldehyde and up to about 1% formaldehyde as a result of the at least one formaldehyde releaser preservative agent. The collected blood sample is storable for at least, or about 7 days without cell lysis and without cell-free nucleic acid degradation of the blood sample due to DNase and RNase activity after blood draw. The method may include isolating the cell free nucleic acids from the stabilized blood sample and testing the isolated cell free nucleic acids from the stabilized blood sample to identify the presence, absence or severity of a disease state.