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Tests and diagnosis
By Mayo Clinic staff
Identifying and determining the cause of interstitial lung disease can be extremely challenging. An unusually large number of disorders fall into this broad category. What's more, the distinction between interstitial lung disorders with identifiable causes and those with no known cause isn't always clear.
In addition, the signs and symptoms of a wide range of medical conditions — among them chronic obstructive pulmonary disease (COPD), heart failure and asthma — can mimic interstitial lung disease, and doctors must rule these out before making a definitive diagnosis.
To help cut through the confusion and rule out other possible illnesses, your doctor is likely to begin with a detailed medical history and physical exam. Once certain conditions have been ruled out, your doctor will recommend tests such as:
- Chest X-ray. Although this is often the first test given in cases of suspected lung problems, a chest X-ray isn't as effective as a computerized tomography (CT) scan in diagnosing interstitial lung disease. It can, however, help eliminate conditions that cause signs and symptoms similar to those of interstitial lung disease, including emphysema and a collapsed lobe of one of the lungs.
- High-resolution computerized tomography (HRCT) scan. Whereas a traditional chest X-ray produces two-dimensional images of your lungs, a CT scan uses an X-ray-sensing unit and a large computer to create cross-sectional images that are far more detailed. An HRCT scan goes even further, showing lung tissue in great detail and providing more information than conventional CT scans do.
- Pulmonary function tests (PFTs). These noninvasive tests check how well your lungs function. For the test, you're usually asked to blow into a simple instrument called a spirometer, which measures how much air your lungs can hold and the flow of air out of your lungs. As scarring becomes worse, you're able to take less air in and blow less out. Some pulmonary function tests also measure the amount of gas exchanged across the membrane between your alveoli and capillary blood vessels.
- Exercise tests. Because symptoms of interstitial lung disease are worse when you're active, your doctor may assess your lung function while you exercise, usually on a stationary bike or treadmill. Although specific tests vary, your blood pressure and blood oxygen levels are usually monitored as the difficulty of the exercise increases.
- Bronchoscopy (transbronchial biopsy). In many cases, interstitial lung disease can be definitively diagnosed only by examining a small amount of lung tissue (biopsy). In a transbronchial biopsy, your doctor passes a flexible, fiber-optic tube (bronchoscope) through your mouth into your lungs and removes one or more tissue samples, each about the size of the head of a pin. These are then examined in a laboratory. Bronchoscopy is performed on an outpatient basis using local anesthesia.
- Bronchoalveolar lavage. In this procedure, your doctor injects salt water (saline) through a bronchoscope into a section of your lung and then immediately suctions it out. The withdrawn solution contains cells from the air sacs. Although bronchoalveolar lavage samples a larger area of the lung than other procedures do, it may not provide enough information to diagnose a specific interstitial lung disease. Instead, doctors often use it to check the progress of a lung disorder or to help determine the best treatment.
- Video-assisted thoracoscopic surgery. When less invasive tests don't yield a specific diagnosis, a thoracic surgeon may perform a surgical lung biopsy. In this procedure, a flexible tube with a camera (endoscope) is inserted through a small incision between your ribs, allowing the surgeon to view your lungs on a video monitor. Surgical instruments are then inserted through another incision, and the surgeon removes thumbnail-sized tissue samples from two or three sites in your lungs.
- King TE, et al. Approach to diagnosis and management of the idiopathic interstitial pneumonias. In: Mason RJ, et al. Murray & Nadel's Textbook of Respiratory Medicine. 4th ed. St. Louis, Mo.: W.B. Saunders; 2005. http://www.mdconsult.com/das/book/body/138709448-3/0/1288/473.html?tocnode=51472932&fromURL=473.html#4-u1.0-B0-7216-0327-0..50056-2_2996. Accessed May 20, 2009.
- Raghu G. Interstitial lung disease. In: Goldman L, et al., eds. Goldman: Cecil Medicine. 23rd ed. Philadelphia, Pa.: Saunders Elsevier; 2007. http://www.mdconsult.com/das/book/body/138709448-4/843693028/1492/374.html#4-u1.0-B978-1-4160-2805-5..50097-5--cesec72_3869. Accessed May 20, 2009.
- King TE. Approach to the adult with interstitial lung disease. http://www.uptodate.com/home/index.html. Accessed May 20, 2009.
- Interstitial lung diseases. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/sec05/ch055/ch055a.html. Accessed May 20, 2009.
- Aggarwal N, et al. Interstitial lung disease. In: Nilsson K, et al. The Osler Medical Handbook. Philadelphia, Pa.: Saunders Elsevier; 2006. http://www.mdconsult.com/das/book/body/142440259-3/850406526/1387/103.html#4-u1.0-B0-323-03748-8..50092-0_1514. Accessed May 20, 2009.
- Possible side effects of radiation therapy. American Cancer Society. Accessed May 20, 2009.
- King TE. Treatment of idiopathic pulmonary fibrosis. http://www.uptodate.com/home/index.html. Accessed May 20, 2009.
- Rosenow EC (expert opinion). Mayo Clinic, Rochester, Minn. May 31, 2009.
