Diagnostic implications of positive avian serology in suspected hypersensitivity pneumonitis

The diagnostic evaluation of patients with interstitial lung disease (ILD) often involves serologic assessment for identifiable causes such as hypersensitivity pneumonitis (HP). While not on its own defining of HP, precipitin serologies are often obtained to support clinical suspicion if other findings are inconclusive. We studied the clinical relevance of positive avian serology in patients undergoing ILD evaluation.

We identified individuals with positive avian serology (>53.3 mg/L) and undifferentiated ILD seen at our institution over a three-year period. Clinical, laboratory, pathologic, and radiologic findings were evaluated for consensus HP diagnosis by two expert pulmonologists, blinded to presenting serology levels.

Ninety-one ILD subjects with positive avian serology were identified; mean age was 62.7 ± 15.3 years with a slight male predominance (56%). Forty-nine (54%) received a consensus HP diagnosis. Those with HP had higher mean avian serology titer (95.0 ± 38.7 mg/L vs. 68.3 ± 16.7, (P < 0.0001). Never-smokers also had higher titers compared to prior or active smokers (P = 0.0008). Positive avian protein exposure (P < 0.0001, OR 21.3 (6.4-87)), DLCO% (P = 0.04, unit OR 0.96 (0.92-0.99)), and increasing serology titer (P < 0.015, unit OR 1.03 [1.01-1.06]) were independent predictors of HP diagnosis.

Among patients with positive avian serology, those with higher titers were more likely to have HP diagnosis. Nonsmokers also manifested higher titers compared to those with smoking history. These results may guide the usage and interpretation of avian serology screening in the initial assessment of suspected HP.