Clinical utility of YKL-40 for understanding pathophysiology of obstructive airway disorders.

Background: Chitinase-3-like protein 1 (YKL-40) has been reported as a biomarker of neutrophilic airway inflammation in obstructive airway disorders. However, the pathophysiological features of YKL-40 remain unclear. The aim of the study is to evaluate the associations between YKL-40 and clinical features in patients with asthma, chronic obstructive pulmonary disease (COPD), or asthma-COPD overlap (ACO).

Methods: Serum and sputum YKL-40 levels were measured in 46 asthmatics, 35 COPD, and 32 ACO patients.

Results: Serum YKL-40 levels were elevated in the COPD and ACO patients, and sputum YKL-40 levels were higher in the COPD patients compared to the asthmatics. Both serum and sputum YKL-40 levels positively correlated with sputum neutrophils. Only serum YKL-40 levels negatively correlated with FEV₁ (%predicted), FEV₁/FVC, and annual decline in FEV₁. In 15 patients whose paired serum samples were obtained within 6 months, changes in serum YKL-40 levels showed a significant positive correlation with those in FEV₁. Furthermore, patients who had experienced exacerbations either in the past year or the following year showed significantly greater serum, but not sputum, YKL-40 levels. Sputum YKL-40 levels showed significant correlations with scores on the COPD assessment test and modified Medical Research Council dyspnea scale.

Conclusions: Serum and sputum YKL-40 may reflect distinct clinical features in obstructive airway disorders. Serum YKL-40 may provide beneficial information on predicting obstructive neutrophilic inflammation and exacerbations, whilst sputum YKL-40 may offer valuable insights for evaluating ongoing symptoms. Concomitant measurement of YKL-40 in serum and sputum might be more useful than individual measurement.