Moreover, in the GINA step 4 + 5 group, serum periostin levels were positively correlated with age (rs = 0.29, P = 0.009), age at asthma onset (rs = 0.316, P = 0.004), FeNO levels (rs = 0.226, P = 0.016), peripheral blood eosinophil counts (rs = 0.398, P < 0.001), and the Th2-high to Th2-low ratio (rs = 0.241, P = 0.03), but were negatively correlated with FVC (rs = − 0.29, P = 0.009), FEV1 (rs = − 0.295, P = 0.008) and MMF (rs = − 0.286, P = 0.01) (Additional file 1: Table S1). This evidence concerns the gene POSTN and asthma.