cfDNA (cell-free DNA, in aging)

Cell-free DNA refers to short (typically 140-200 bp mono-nucleosome and 300-400 bp di-nucleosome) double-stranded DNA fragments released into plasma by apoptotic and necrotic cells. It is quantified by fluorometry (Qubit), qPCR or droplet digital PCR after column-based plasma extraction, with healthy adult plasma concentrations roughly 1-10 ng/mL. cfDNA rises with chronological age, chronic inflammation ("inflammageing"), strenuous exercise, sepsis, autoimmune disease, trauma and active malignancy, and is regarded as an aggregate readout of tissue turnover and immune activation. The 2018 Moss et al. methylation-deconvolution work showed that cell-type-specific methylation signatures allow tissue-of-origin mapping of cfDNA, enabling non-invasive quantification of cell death in specific organs. cfDNA forms the analytic substrate for liquid-biopsy oncology, transplant rejection monitoring, non-invasive prenatal testing and multi-cancer early detection. Major confounders are haemolysis during phlebotomy and delayed plasma separation.