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Diagnosis of hypersensitivity pneumonitis (extrinsic allergic alveolitis)

Talmadge E King, Jr, MD
Section Editor
Kevin R Flaherty, MD, MS
Deputy Editor
Helen Hollingsworth, MD


Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is a complex syndrome of varying intensity, clinical presentation, and natural history rather than a single, uniform disease [1-11]. Numerous inciting agents have been described including, but not limited to, agricultural dusts, bioaerosols, microorganisms (fungal, bacterial, or protozoal), and certain reactive chemical species. (See "Epidemiology and causes of hypersensitivity pneumonitis (extrinsic allergic alveolitis)".)

The diagnostic evaluation of patients with suspected HP will be reviewed here. The classification, clinical manifestations, and treatment of HP are discussed separately. (See "Classification and clinical manifestations of hypersensitivity pneumonitis (extrinsic allergic alveolitis)" and "Treatment, prevention, and prognosis of hypersensitivity pneumonitis (extrinsic allergic alveolitis)".)

Prompt diagnosis of HP is important, as the disease is reversible when diagnosed early in its course. Correct diagnosis is based upon exposure history, clinical assessment, radiographic and physiologic findings, and, if possible, the result of removal of the patient from the suspected etiologic exposure. Other tests, such as bronchoalveolar lavage (BAL) and lung biopsy, are helpful in ruling out other potential diagnoses and in lending further support to the diagnosis of HP. Of note, cigarette smokers have a lower risk of developing HP than nonsmokers because of diminished antibody production following exposure to inhaled antigens. (See "Epidemiology and causes of hypersensitivity pneumonitis (extrinsic allergic alveolitis)".)


Several different diagnostic criteria for HP have been proposed [8,12,13]. All have significant problems that limit their utility:

All were developed before the common use of high resolution computed tomography (CT) scanning and bronchoalveolar lavage

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Literature review current through: Nov 2017. | This topic last updated: Sep 09, 2016.
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