OBJECTIVE: The abnormal formation and insufficient clearance of neutrophil 
extracellular traps (NETs) has been reported to be involved in the pathogenesis 
of lupus nephritis (LN). The abnormal regulation of NETs may contribute to 
increases in the levels of circulating cell-free DNA (cfDNA). The present study 
tested the hypothesis that elevated plasma cfDNA levels are related to LN.
METHODS: Fifty-four systemic lupus erythematosus (SLE) patients and 43 control 
subjects were included in this study. The cfDNA concentrations were measured 
using the Picogreen Kit, the low-density granulocyte (LDG) percentage in 
peripheral blood mononuclear cells (PBMCs) was tested using a flow cytometer and 
the DNase I activity was measured according to the radial enzyme-diffusion 
method.
RESULTS: The mean cfDNA concentration in the SLE group was 236.66±40.09 ng/mL, 
which was significantly higher than that observed in the healthy control group 
(187.96±40.55 ng/mL, p<0.0001). Meanwhile, the mean cfDNA concentration in the 
patients with LN was significantly higher than that observed in the patients 
without LN (247.27±46.79 ng/mL vs. 213.56±31.34 ng/mL, p=0.0094), and the mean 
cfDNA concentration in the patients with active LN was significantly higher than 
that observed in the patients with inactive LN (254.22±50.16 ng/mL vs. 
215.93±29.10 ng/mL, p=0.0349). In the SLE group, the cfDNA concentration was to 
positively correlate with the quantitative 24-hour urinary protein (r=0.350, 
p=0.013), LDG (r=0.6361, p=0.0019) and neutrophil (r=0.5990, p<0.0001) levels 
and inversely correlate with the albumin level (r=-0.500, p<0.0001) and 
endogenous creatinine clearance rate (r=-0.354, p=0.044). Compared to that 
observed in the control group, the SLE group exhibited a significantly increased 
percentage of LDGs in PBMCs and a significantly decreased DNase I activity.
CONCLUSION: Our data indicate that elevated plasma cfDNA concentrations may be 
associated with active LN and partially attributed to the abnormal regulation of 
NETs in SLE patients, thus suggesting that NETs constitute an intrinsic link 
between cfDNA and active LN.