There are a number of different ways to diagnose PAH. Blood tests may be used to check oxygen levels and liver and kidney function and to identify the presence of collagen vascular disease, thyroid problems, signs of infection, or HIV antibodies.
One test can check for levels of brain natriuretic peptide to assess the strain on the heart and monitor response to treatment. In addition, chest X-rays can be used to check the right ventricle of the heart and the pulmonary arteries for signs of enlargement. They can also reveal the presence of emphysema or scarring (interstitial fibrosis) of the lungs. An electrocardiogram or echocardiogram may also be used to monitor heart function.
To focus on the lungs, pulmonary function tests measure oxygen capacity in the lungs and their ability to exchange oxygen. A nuclear scan (also called a ventilation/perfusion, or V/Q, scan) tests for blood clots in the lungs by producing a picture of air and blood flow to the lungs. With this test, the patient inhales a small dose of radioactive marker, while another small dose is injected into a blood vessel, to allow imaging of the lungs. The resulting images give doctors an idea of lung health.
In addition, a six-minute stress test may be required to show the patient's tolerance for exercise.
One of the most definitive diagnostic tests for PAH is right-heart catheterization, which directly measures the pressure inside the patient's pulmonary arteries. It should be performed at least once in any patient who might have PAH. During the test, doctors insert a thin rubber tube, or catheter, through a large vein in the patient's groin or neck. They then pass the catheter up into the patient's heart to measure blood pressure in the right side of the heart and lungs.
A vasodilator study is required for patients who have been diagnosed with PAH to determine how much their pulmonary blood vessels can relax over a brief period of time. Its main purpose is to screen for patients who might respond favorably to treatment with calcium channel blockers. The test can also help determine the patient's prognosis. With a right-heart catheter in place, the patient is given drugs that relax the pulmonary arteries. The test drug is given to the patient in higher and higher doses, pausing after each dose to see how the patient reacts. Once a significant response occurs, or the side effects become intolerable, the test is considered complete.