How do you diagnose hypersensitivity pneumonitis?
No single test can make a definite diagnosis of HP. The key is to relate some specific exposure or activity to episodes of symptoms. The chest x ray may be normal in the acute stage, but later may show a hazy appearance that looks like “ground glass.” There may be linear or rounded shadows in the central parts of the lungs. Studies of lung function in the acute stage typically show abnormally small lung volume. The ability to breathe at a fast rate is impaired. Blood from an artery typically has a low level of oxygen. Later, when the lungs have begun to scar, the airways (breathing tubes) are obstructed and the rate of air flow is reduced. Some experts believe that skin testing can help diagnose HP and show which particular antigen is causing the symptoms. Small amounts of several suspect antigens are injected just beneath the surface of the skin, usually on the arm or back, and the reactions compared to that caused by injecting a harmless salt solution. Another diagnostic test is to p
