Validation of inhalation provocation test in chronic bird-related hypersensitivity pneumonitis and new prediction score

Rationale: Hypersensitivity pneumonitis (HP) is an immunologically mediated lung disease induced by the inhalation of any of a wide variety of antigens. For example, bird-related HP (BRHP) results from the inhalation of avian antigens. The clinical features of chronic HP, including imaging and histological findings, are similar to those of idiopathic pulmonary fibrosis. Despite its status as the "gold standard," the inhalation provocation test (IPT) is rarely performed, because the methods and the criteria are not standardized. In 2000, we reported the utility of IPT for pigeon dropping extracts.

Objectives: The purpose of the current study was to validate the utility and safety of the test, and to differentiate chronic HP from other interstitial lung diseases.

Methods: A total of 28 patients with chronic BRHP and 19 control subjects were evaluated in this retrospective study. We validated the previous criteria and proposed new criteria using prediction scores.

Measurements and main results: In the IPT using pigeon dropping extracts, the previous criteria showed a sensitivity of 78.6% and a specificity of 94.7% in this retrospective study. The increases in the peripheral white blood cell count and C-reactive protein levels are good indicators of a positive response to the inhalation challenge. We propose the use of the IPT prediction score (∆WBC [%] + 2 × ∆P[a - a]O2 [mm Hg], where WBC is white blood cell) and the prediction rule, which showed high sensitivity and specificity values of 92.9 and 94.7%, respectively. Two (1.5%) out of a total of 130 subjects who underwent the tests required treatment after the challenge.

Conclusions: The IPT is a useful and safe tool for the diagnosis of chronic HP. The IPT prediction score that we have proposed has high sensitivity and specificity in the diagnosis of chronic BRHP.