APOA1 and non-proliferative diabetic retinopathy: After identifying many differentially expressed proteins in patient serum and VH, Kim et al. validated a set of twenty-seven biomarkers of mild stage NPDR, including apolipoprotein A-I (APOA1), α-2-macroglobulin (A2M), complement factor H (CFH), and prothrombin (F2), using multiple reaction monitoring (MRM) assays [82].