FGF21 and non-proliferative diabetic retinopathy: Serum FGF21 concentrations in patients with PDR (n = 49; 669.4 ± 89.2 pg/mL) or NPDR (n = 34; 631.9 ± 73.8 pg/mL) were significantly higher than those in patients without retinopathy (n = 34; 326.8 ± 81.6, P < 0.001).