The use of specific inhalation challenge in hypersensitivity pneumonitis

Purpose of review The diagnosis of hypersensitivity pneumonitis remains a dilemma because of the absence of any characteristic features able to distinguish it from other interstitial lung diseases. We analyze the current role of the specific inhalation challenge (SIC) in the diagnosis of this entity. Recent findings Few descriptions of the use of SIC for the diagnosis of hypersensitivity pneumonitis have been published in recent years. In fact, hypersensitivity pneumonitis is still diagnosed on the basis of clinical criteria, as there is no agreement on the diagnostic utility of SIC. Two major reviews carried out in the past year have concluded that this test is not standardized and is usually unnecessary; however, a third study found that the test can indeed recreate the symptoms and functional abnormalities in the laboratory, and may therefore be of considerable use in the diagnosis of hypersensitivity pneumonitis. Summary Hypersensitivity pneumonitis remains a diagnostic challenge. Given that the main cause of the disease is sensitization and hyper-responsiveness to specific antigens in susceptible individuals, SIC is an obvious candidate as the gold standard for diagnosis of this entity. The present review analyzes the reasons for the test's limited use, assesses its diagnostic utility, and proposes a basis for its standardization.