Evaluation of Circulating YKL-40 Levels in Idiopathic Interstitial Pneumonias

YKL-40 is a novel biomarker in diseases with inflammation, fibrosis and tissue remodelling. Previously, circulating YKL-40 was shown to be elevated in patients with idiopathic pulmonary fibrosis (IPF) and was associated with survival. To compare YKL-40 serum levels between IPF and other interstitial pneumonias such as non-specific interstitial pneumonia (NSIP), smoking-related interstitial lung disease (SR-ILD) and cryptogenic organising pneumonia (COP). Serum YKL-40 levels were measured in 124 healthy controls and 315 patients. Serial measurements were available in 36 patients with IPF and 6 patients with COP. Serum YKL-40 levels were elevated in all patient groups compared to controls (p < 0.0001), and highest levels were found in the most fibrotic diseases, which showed worst prognosis. YKL-40 is highly elevated in fibrotic interstitial pneumonias and may reflect the degree of activity of the fibrogenic process. Remarkably, levels remain high in IPF, but can decrease in other interstitial pneumonias, which appears to be related to a better prognosis.