Cell-free dna in the blood originates from the natural destruction of cells through necrosis, apoptosis, or normal cell turnover.

“when cells um are destroyed right either through necrosis or apoptosis or just you know there's a lot of cell turnover right of cells that replicate right especially epithelial cells blood cells uh and so on um um as those again as the kind of natural biochemistry destroys them some of the DNA from the nucleus ends up in circulation right”