11th May 2025

Investigations

PH investigations usually begin when the patient presents with dyspnoea and includes chest x-ray, transthoracic echocardiogram, and possibly pulmonary function tests at this stage (Table 2 describes findings related to PH and its associated conditions). Echocardiogram estimates systolic pulmonary artery pressures and so is useful in raising clinical suspicion but is not considered diagnostic. All patients should go on to have right cardiac catheterisation to accurately measure pulmonary pressures and provide definitive diagnosis. Right heart catheterisation also allows for measurement of haemodynamic parameters (such as cardiac output/index atrial pressures, pulmonary vascular resistance and pulmonary artery saturations) which are important prognostic markers.

Blood tests performed in the initial patient work-up are aimed at alternative causes of dyspnoea and eventually to investigate secondary causes of PH. Labs include full blood count, liver function tests, clotting studies, thyroid function tests, autoantibodies (anti-nuclear, anti-dsDNA, anti-centromere), HIV serology, BNP (B-type natriuretic peptide) or NT-proBNP (N-terminal proBNP). BNP correlates to the severity of right cardiac dysfunction and is used as a marker of prognosis and mortality in patients with PAH.

If obstructive sleep apnoea (OSA) is suspected, overnight oximetry should be performed. 

If no secondary aetiologies are identified, a diagnosis of idiopathic PAH is made.

Table 2: Clinical findings of PH and its associated conditions

In PAH (WHO Group 1), vasodilator testing can be used to identify a small subset of patients who may benefit from treatment with calcium-channel blockers (CCB’s). Pulmonary pressures are measured before and after administration of vasodilators (inhaled nitric oxide, intravenous epoprostenol, or intravenous adenosine). If the patient has already progressed to right heart failure, vasodilator testing should not be performed.

A 6-minute-walk-test (6MWT) is performed in all patients with PH and is used to track management and guide prognosis. This test assesses how far the patient can walk in 6-minutes and has an inverse correlation with the functional class of the patient.