Figure 2
![Figure 2](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2F1297-9716-44-46/MediaObjects/13567_2013_Article_256_Fig2_HTML.jpg)
Threshold identification by Receiver Operator Curves (ROC) analysis. Receiver Operator Curves (top graph) and estimated cut-off (bottom graph) for (A) Blood VI, (B) Blood qRT-PCR, (C) OPF VI and (D) OPF qRT-PCR. The cut-off is defined as the value that maximizes the sensitivity + specificity.