cfDNA (cell-free DNA, in aging)

Cell-free DNA (cfDNA) is short fragments of DNA floating in your blood plasma. They are released by cells that die, by apoptosis or necrosis. (The fragments are typically 140-200 bp from a single nucleosome, or 300-400 bp from two.) Labs measure it by fluorometry (Qubit), qPCR, or droplet digital PCR, after extracting it from plasma. Healthy adults run about 1-10 ng/mL. cfDNA rises with age, chronic inflammation ('inflammaging'), hard exercise, sepsis, autoimmune disease, trauma, and active cancer. So it is seen as an overall readout of tissue turnover and immune activity. A 2018 study (Moss et al.) showed something powerful: each cell type has its own methylation signature, so you can map which organ the cfDNA came from. That allows non-invasive measurement of cell death in specific organs. cfDNA is the raw material for liquid-biopsy cancer detection, transplant-rejection monitoring, non-invasive prenatal testing, and multi-cancer early detection. The main pitfalls: red-cell breakdown (hemolysis) during the blood draw, and delayed plasma separation.

Last reviewed: June 22, 2026

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