- Background The animal model of stroke that is most frequently used is a rat model of focal brain ischemia caused by middle cerebral artery occlusion (MCAO). Several studies have reported a link between levels of cell-free DNA (CFD) and neurologic outcome in human stroke. The purpose of this study was to assess brain injury and measure CFD levels in 2 models of MCAO in rats, and to determine whether brain injury correlates with CFD. Methods A total of 60 rats were used for this study. Twenty rats underwent a sham procedure, 20 rats had MCAO using a monofilament, and 20 rats had MCAO with a silicon-coated filament. Groups were further divided into 2 subgroups. In 1 subgroup of 10 rats, neurologic performance [measured as a neurologic severity score, (NSS)] was measured at 1 and 24 hours after the procedure, and brain edema and infarct volume were determined at 24 hours. In the second subgroup of 10 rats, CFD was measured at 0, 1, 2, 4, 8, 12, and 24 hours and at 2, 3, 4, and 5 days. Neurologic performance (measured as a NSS) was measured at 1 and 24 hours after the procedure. Results The main finding was a significant increase in CFD levels observed 24 hours after the onset of MCAO. The correlation between the total infarct volume and CFD levels of the 3 groups was R=0.78, P<0.0001. Brain edema and NSS also were strongly correlated with CFD levels at 24 hours after MCAO (R=0.91, P<0.0001 and R=0.73, P<0.0001, respectively). Conclusions We found that CFD levels correlate well with the extent of ischemic injury, brain edema, and neurologic outcome in rats 24 hours post-MCAO. We have also shown that CFD correlates well with the expected temporal progression of ischemic injury. These findings place CFD in a unique place as a biomarker for stroke, both experimentally and possibly clinically.