Levels of YKL-40 in pleural effusions and blood from patients with pulmonary or pleural disease

Background: YKL-40 (a chitinase-like protein) is an inflammatory biomarker that is associated with lung injury pathogenesis. We aimed to identify the diagnostic values of YKL-40 in pleural effusions and to evaluate circulating YKL-40 levels during multiple etiological pulmonary/pleural diseases and the role of YKL-40 as a monitoring marker of inflammatory pulmonary disease.

Methods: Pleural YKL-40 (n=197), YKL-39 (the most homologous chitinase-like protein to human YKL-40), and conventional pleural marker levels were measured in patients with pulmonary/pleural disease. Additionally, serum YKL-40 and YKL-39 levels were analyzed in both patients and controls (n=432) and serially monitored in patients with asthma (n=27) or pneumonia (n=22).

Results: Pleural YKL-40 levels were higher than those in the serum and highest in tuberculous pleural effusions (TPEs; 1181 ng/mL), followed by parapneumonic, malignant, and cardiogenic effusions (560 ng/mL). The diagnostic accuracy of pleural YKL-40 (0.78) for discriminating between tuberculous and malignant effusion was comparable to or greater than those of YKL-39, total protein, C-reactive protein and CYFRA 21-1, and lower than those of adenosine deaminase (p<0.05) and carcinoembriogenic antigen (p=0.05). Serum YKL-40 levels were higher in the pneumonia group than in the cancer, asthma, or control groups. Following treatment, serum YKL-40 levels were more greatly reduced in pneumonia patients than in asthma patients. Serum YKL-39 levels did not differ between patients and controls.

Conclusions: Pleural YKL-40 levels are elevated in TPEs and have fairly good diagnostic efficacy for detecting TPEs. However, adenosine deaminase is more efficient for detecting TPEs than pleural YKL-40. Serum YKL-40 levels are highest during pneumonia compared to common pulmonary/pleural diseases and are more useful for monitoring pneumonia than asthma.