Background: Right ventricular (RV) fibrosis is common in patients with repaired tetralogy of Fallot (rTOF). Although accumulating evidence indicates the role of circulating biomarkers of collagen metabolism in left ventricular fibrosis, rTOF data are lacking. This study examined the expression profile and clinical relevance of circulating biomarkers of collagen type I metabolism in rTOF patients. Methods: Serum biomarkers of collagen type I synthesis (carboxy-terminal propeptide of procollagen type I, PICP), degradation (carboxy-terminal telopeptide of collagen type I, CITP), and enzymes regulating collagen degradation (matrix metalloproteinases, and type I tissue inhibitor, TIMP-1) were measured in 70 rTOF and 91 control adults. All patients had complete clinical data and received cardiovascular magnetic resonance scans with late gadolinium enhancement (LGE). Results: Compared to the controls, rTOF patients had higher PICP levels (p150 mL/m(2) (beta=40.52, p=0.016), RV LGE score (beta=3.94, p=0.008), and age (beta=-1.77, p=0.011) as independent correlates of circulating PICP levels. Conclusions: Patients with rTOF exhibited a profibrotic state with excessive collagen type I synthesis and dysregulated degradation. Elevated circulating PICP levels might reflect RV fibrosis, and link to adverse markers of clinical outcome. (C) 2012 Elsevier Ireland Ltd. All rights reserved.