Top tests for following the progression of IPF

Idiopathic pulmonary fibrosis (IPF) is a scarring process that damages the lung and makes it hard for patients to breathe. Over time, their breathlessness worsens. While there are many medical tests that physicians use to follow patients along the progression of pulmonary fibrosis, there are four primary tools that have proven most helpful.

“Breathlessness is caused by patients’ lungs being smaller than they should be. With IPF, because their lungs are smaller and stiffer, the ability to take a bigger breath is impaired. The way they compensate is by taking more breaths,” said Talmadge E King, Jr., MD, chair of the Department of Medicine at the University of California, San Francisco.

“To measure how well IPF patients’ lungs are working, lung function testing is performed. This combination of tests measures how large the patient’s lungs are, how much air the patient can blow out of their lungs, and how the lungs send oxygen to the blood,” King said.

From this test, the physician is able to determine the patient’s forced vital capacity (FVC), or the amount of air the patient can force out of their lungs. This simple test can be conducted in physicians’ offices every three to six months. “We know that following the FVC level helps predict a patient’s clinical course and relates to the patient’s long-term survival,” King said.

Another test that is important for physicians to conduct is the diffusing capacity test. This test helps determine the overall ability of the lung to transport gas into and out of the blood. “In the lung function lab, we give a very small amount of carbon monoxide for the patient to inhale. The patient takes a deep breath, holds that breath for about 10 seconds, and blows out. The amount of carbon monoxide that went into the lung versus how much came back out allows the determination of how much of the gas moves from the lung to the blood,” King said.

The diffusing capacity test is an important tool for physicians, since the diffusing capacity is very sensitive and an abnormal gas exchange is one of the “first things that is reduced in fibrotic lung diseases,” King said.

Another common test to follow the progression of the disease is the six-minute walk test. The goal is for the IPF patient to quickly walk as far as possible in six minutes on a hard, flat surface. The patient can rest, and then continue walking, if needed. “Most healthy people walk 400 to 700 m, whereas people with lung fibrosis may walk a shorter distance, maybe 150 to 400 m,” King said.

At rest or during the walk test, pulse oximetry (a sensor on the skin that measures the amount of arterial oxygen saturation) may be used as a noninvasive measurement of the ability of lungs to oxygenate the blood.

Another test utilized – but not as commonly – to diagnose and follow the progression of the disease is a high-resolution computed tomography (HRCT) of the lungs. The HRCT scan offers a highly detailed lung image, to help physicians identify patterns in lung tissue that may indicate IPF. “We conduct the HRCT scan at the initial diagnosis, and then maybe yearly after that,” King said.