Diagnosis

Identifying and determining the cause of interstitial lung disease can be challenging. A large number of disorders fall into this broad category. In addition, the signs and symptoms of a wide range of medical conditions can mimic interstitial lung disease, and doctors must rule these out before making a definitive diagnosis.

Some of the following tests may be necessary.

Laboratory tests

• Blood tests. Certain bloodwork can detect proteins, antibodies and other markers of autoimmune diseases or inflammatory responses to environmental exposures, such as those caused by molds or bird protein.

Imaging tests

• Computerized tomography (CT) scan. This imaging test is key to, and sometimes the first step in, the diagnosis of interstitial lung disease. CT scanners use a computer to combine X-ray images taken from many different angles to produce cross-sectional images of internal structures. A high-resolution CT scan can be particularly helpful in determining the extent of lung damage caused by interstitial lung disease. It can show details of the fibrosis, which can be helpful in narrowing down the diagnosis and in guiding treatment decisions.
• Echocardiogram. A sonogram for the heart, an echocardiogram uses sound waves to visualize the heart. It can produce still images of your heart's structures, as well as videos that show how your heart is functioning. This test can evaluate the amount of pressure occurring in the right side of your heart.

Pulmonary function tests

• Spirometry and diffusion capacity. This test requires you to exhale quickly and forcefully through a tube connected to a machine that measures how much air your lungs can hold, and how quickly you can move air out of your lungs. It also measures how easily oxygen can move from the lungs into the bloodstream.
• Oximetry. This simple test uses a small device placed on one of your fingers to measure the oxygen saturation in your blood. It may be done at rest or with activity to monitor the course and severity of lung disease.

Lung tissue analysis

Often, pulmonary fibrosis can be definitively diagnosed only by examining a small amount of lung tissue (biopsy) in a laboratory.

The tissue sample may be obtained in one of these ways:

• Bronchoscopy. In this procedure, your doctor removes very small tissue samples — generally no larger than the head of a pin — using a small, flexible tube (bronchoscope) that's passed through your mouth or nose into your lungs. The risks of bronchoscopy are generally minor — most often a temporary sore throat and hoarseness from the bronchoscope — but the tissue samples are sometimes too small for an accurate diagnosis.
• Bronchoalveolar lavage. In this procedure, your doctor injects about a tablespoon of salt water through a bronchoscope into a section of your lung, and then immediately suctions it out. The solution that's withdrawn contains cells from your air sacs. Although bronchoalveolar lavage samples a larger area of the lung than other procedures do, it may not provide enough information to diagnose pulmonary fibrosis.
• Surgical biopsy. Although this is a more invasive procedure with potential complications, it's often the only way to obtain a large enough tissue sample to make an accurate diagnosis. While you are under general anesthesia, surgical instruments and a small camera are inserted through two or three small incisions between your ribs. The camera allows your surgeon to view your lungs on a video monitor while removing tissue samples from your lungs.