Antigen avoidance tests for diagnosis of chronic hypersensitivity pneumonitis

Background: Chronic hypersensitivity pneumonitis (HP) is induced by the inhalation of specific antigens. Patients with chronic HP may be able to improve their prognosis by avoiding these antigens. Chronic HP is often difficult to distinguish from idiopathic interstitial pneumonias (IIPs). Objective: This study was performed to find out how antigen avoidance tests contribute to the diagnosis of chronic HP. Methods: A retrospective analysis was conducted on 265 patients who underwent 2-week antigen avoidance tests between April 2002 and March 2012. The patients were classified into the following categories: acute HP, chronic HP, collagen vascular disease-associated interstitial pneumonia (CVD-IP), lung dominant connective tissue disease (LD-CTD), and IIPs. The following seven clinical parameters were evaluated: vital capacity, alveolar-arterial oxygen pressure difference, Krebs von den Lungen-6, surfactant protein-D, white blood cell count, C-reactive protein, and body temperature. These parameters were compared between the chronic HP group and a control group consisting of CVD-IP, LD-CTD, and IIPs. Results: One-hundred and ninety-six patients with chronic HP and 43 control subjects were evaluated. All clinical parameters improved significantly in the chronic HP group but showed no significant changes in the control group. Four of the parameters changed significantly compared with the control group. Diagnostic criteria established using these data had a sensitivity of 51.0% and a specificity of 80.7%. Conclusions: It was difficult to diagnose chronic HP based solely on 2-week antigen avoidance tests; however, improved clinical parameters among patients supported the diagnosis of HP. Copyright (C) 2015 The Japanese Respiratory Society. Published by Elsevier B.V. All rights reserved.