CHI3L1 and asthma: In patients with asthma, serum YKL-40 was increased in those with the most severe asthma compared with the remaining patients (GINA 1–4); median (25–75 percentile) serum YKL-40: intermittent 37 μg/L (28–50 μg/L); mild persistent 40 μg/L (29–51 μg/L); moderate persistent 39 μg/L (30–53 μg/L); and severe persistent 46 μg/L (33–63 μg/L), p=0.009) (Fig. 1).