Pulmonary vascular remodelling and inflammation have been implicated in pulmonary arterial hypertension (PAH). YKL‐40, a marker of tissue remodelling and inflammation, has recently been recognized as a risk predictor of cardiovascular and inflammatory diseases. The study aimed to investigate a potential role of YKL‐40 in predicting prognosis in idiopathic PAH (IPAH).

Plasma YKL‐40 levels were measured in 82 IPAH patients without current or previous PAH‐specific treatment during right heart catheterization and in 54 healthy volunteers. Concurrent data included clinical, haemodynamic and biochemical variables.

Plasma YKL‐40 levels were increased in IPAH patients compared with control subjects (median, interquartile range: IPAH: 24.90, 17.68–39.78 ng/mL; controls: 16.58, 14.20–19.64 ng/mL; P < 0.001). YKL‐40 levels correlated with cardiac index (r = −0.244, P = 0.027) and N‐terminal pro‐brain natriuretic peptide (NT‐proBNP, r = 0.263, P = 0.017). After a median follow‐up of 578 days, YKL‐40 outperformed NT‐proBNP, uric acid, and 6‐min walk distance in receiver operating characteristic (ROC) analyses in predicting both clinical worsening (area under the curve (AUC) 0.681) and death (AUC 0.717). Compared with patients with YKL‐40 below the ROC‐derived cut‐off point (24.5 ng/mL), the high YKL‐40 group showed higher pulmonary vascular resistance and serum uric acid levels, and showed more clinical worsening events and deaths in Kaplan–Meier analyses. Plasma YKL‐40 was independently associated with clinical worsening in univariate and multivariate Cox analyses (all P < 0.05).

Plasma YKL‐40 might serve as a promising indicator of disease severity and prognosis in patients with IPAH.