NPPB and idiopathic pulmonary arterial hypertension: NTproBNP levels were markedly higher in both IPAH (316.8 ± 45.7 ng/L) and CTD-PAH patients (329.3 ± 65.0 ng/L) vs. controls (78.0 ± 11.5 ng/L; p < 0.001; Figure 1A,B).