How much circulating cell-free DNA can I expect from samples, and how can I quantify the yield?

Typically, a yield of 7.5 ng/ml plasma or urine can be expected. This yield results in <1 ng/µl eluate. However, the yield will vary from sample to sample, due to large donor-dependent variations in circulating cell-free DNA (ccfDNA) concentration in plasma: variation can be approximately 20-fold for healthy blood donors and 1000-fold for both clinical samples and urine.

Because of the very low concentrations of ccfDNA in sample materials (e.g., 0.1 ng/µl eluate is not unusual), measurement of DNA with a spectrophotometer is not recommended. A sensitive and accurate fluorescence-based quantitation assay or a real-time PCR assay should be used for ccfDNA-concentration determination.