SPP1 and asthma: The ROC curve analysis of serum OPN was performed for differentiating individuals with asthma from HCs with an area under the curve (AUC) value of 0.757 (P < 0.001) and an optimal cutoff of 1488.51 pg/mL (log-transformed data as 3.17) at 75.4% sensitivity and 66.1% specificity (Fig. 1d).