Objectives To assess the relationship of C-reactive protein (CRP) to clinical outcome and mortality in adults with pulmonary arterial hypertension (PAH) associated with congenital heart disease (CHD-PAH).

Background Approximately 5–10% of adults with congenital heart disease (ACHD) develop PAH, which in turn is associated with substantial morbidity and mortality. Although CRP is known to predict outcome in idiopathic PAH, little is known regarding its prognostic value in CHD-PAH.

Methods We obtained and analysed 1936 CRP values in a total of 225 adults with CHD-PAH (median age at study entry 34.0 years (27.0–41.7); 32.9% male, 35% with Down syndrome), performed over a 12-year period. High CRP values related to infection or blood transfusions were excluded from the analysis.

Results During a median follow-up of 4.8 years (1149 patients-years), 50 patients died. The median CRP concentration on the last assessment was 5.0 mg/L (IQR 2.0–10.0), higher in deceased patients compared with survivors (11.5 mg/L (6.0–23.0) vs 4.0 mg/L (1.5–8.0), p<0.0001). Following univariate Cox regression analysis, CRP emerged as a strong predictor of mortality (HR 1.18; 95% CI 1.11 to 1.26, p<0.0001) and remained significant after adjustment for age, presence of Down syndrome and advanced PAH therapy. Survival–receiver–operator characteristic analysis identified an optimal cut-off value of 10 mg/L. Patients with CRP >10 mg/L had more than a threefold increased risk of death (HR 3.63, 95% CI 2.07 to 6.38, p<0.0001).

Conclusions Serum CRP is a simple but powerful marker of mortality in CHD-PAH patients and should be incorporated in the risk stratification and routine assessment of these patients.