Levels of YKL-40 in pleural effusion and blood from patients with pleuritis.

Introduction: In recent years, there have been a significant increase in the tests and biomarkers available for pleural fluid analysis. YKL-40 is one of the inflammatory biomarkers that is used for this purpose. The aim of our study is to assess the levels and diagnostic values of YKL-40 in patients with different types of pleural effusions (PE).
Materials and Methods: This was a prospective, observational and crosssectional study. Pleural and serum YKL-40 levels were measured using enzyme-linked immunosorbent assay in 119 patients with PEs, including 23 transudates PE, 47 malignant PE, 26 parapneumonic PE (PPPE), 17 paramalignant PE (PME) and 6 tuberculous PE (TBPE).
Result: Median pleural YKL-40 level was higher in exudates (390.3 ng/mL) than in transudates (369.5 ng/mL) (p<0.02). For a cut-off level of 378 ng/mL, it was found to predict exudates with 70% sensitivity and 64% specificity. [area under the curve (AUC)= 0.660, p= 0.01]. Median pleural YKL-40 level was highest in PMEs (407.1 ng/mL) and the lowest in transudates (369.5 ng/ mL) and high levels, with a cut-off value of 396 ng/mL, differentiated PMEs from other subgroups with 65% sensitivity and 68% specificity. (AUC= 0.680, p= 0.02). Median serum YKL-40 level was the highest in PPPEs (351.4 ng/mL) and the lowest in TBPEs (114.2 ng/mL) (p= 0.01). For a cut-off level of 284 ng/mL, it differentiated PPPEs from TBPEs with 61% sensitivity and 100% specificity (AUC= 0.830, p= 0.01). In TBPEs, pleural/serum YKL-40 ratio was strongly related with pleural ADA (r= 1, p= 0.04).
Conclusions: Pleural YKL-40 may be useful for differentiating exudates and detecting PMEs. Serum YKL-40 may be good diagnostic biomarker for differentiating PPPEs and TBPEs. Additionally, measuring serum and pleural YKL-40 and pleural ADA may be reliable way to diagnose TBPEs.