Fig. 4. Quantitative analysis of plasma DNA in the plasma of 400 healthy adults by three methods. While the median plasma DNA concentration of 400 healthy adults determined by duplex real time PCR with internal standard (18.1 ng/mL) was significantly higher than those determined by real time PCR and PicoGreen assay with external standards (8.2 ng/ml and 13.3 ng/ml; Wilcoxon matched-pairs signed-rank test, P=0.0000) (A), there were statistically significant but weak positive correlations among plasma DNA levels determined by these three different methods (B-D).