Due to the lack of typical clinical symptoms,the average delay time for diagnosis of pulmonary hypertension (PH) is longer than 2 years.It is urgent to find biomarkers for PH diagnosis.In this study we investigated whether plasma microRNAs (miRNAs) can be used as biomarkers for PH diagnosis.We used microarray to identify dynamic miRNAs between PH and non-PH patients.The candidate miRNAs were verified using qRT-PCR in a mouse model of PH,which was induced by monocrotaline (MCT) injection.We observed that miR-21,miR-126,miR-145,miR-191 and miR-150 had no differences between control mice and MCT-treated mice;but plasma miR-451 was significantly decreased in the 2 wk-MCT group,with no further decrease in the 4 wk-MCT group.Plasma miR-451 was also markedly decreased in PH patients,whereas miR-21,miR-126,miR-150 and miR-320 did not show differences between 53 PH patients and 54 non-PH patients.Receiver operating characteristic curves (ROCs) were constructed from the patient data to assess the clinical diagnostic values of circulating miR-451 and Doppler echocardiography (D-ECHO).The areas under the curve (AUCs) of ROCs for miR-451 and D-ECHO were 0.710 and 0.766,respectively.Combination of miR-451 and D-ECHO with AUC of 0.825 was superior to the use of either miR-451 or D-ECHO alone for PH diagnosis.In conclusion,plasma miR-451 has a moderate diagnostic value in PH comparable to that of D-ECHO,and the combination of miR-451 with D-ECHO has better diagnostic value than either method alone,which may have implications for PH diagnosis.