Hypersensitivity Pneumonitis Serologic Panel
A comprehensive hypersensitivity pneumonitis serologic panel should include serum IgG antibody testing against common environmental antigens relevant to the patient's specific exposures, with ELISA being the preferred testing method. 1
What to Include in the Panel
The panel composition should be tailored to the patient's exposure history rather than ordering a generic "shotgun" panel. Based on the 2020 ATS/JRS/ALAT guideline, serum IgG testing is suggested for identifying potential HP-associated antigens, though with very low confidence in effects 1.
Core Antigens to Consider Based on Exposure:
Bird-related exposures:
- Pigeon serum proteins
- Budgerigar (parakeet) proteins
- Other avian antigens based on specific bird exposure 2
Home/environmental exposures:
- Trichosporon asahii (summer-type HP, particularly relevant in Japan but can occur elsewhere)
- Mold antigens (Aspergillus species, Penicillium species)
- Thermophilic actinomycetes 2
Occupational exposures:
- Farmer's lung: thermophilic actinomycetes, Saccharopolyspora rectivirgula
- Metalworking fluid HP: mycobacterial antigens, fungal contaminants
- Humidifier lung: various bacterial and fungal contaminants 3, 2
How to Order
Order serum IgG testing using ELISA methodology - this performs better than precipitin testing for distinguishing HP from other interstitial lung diseases (sensitivity 83%, specificity 68%) 1. The guideline emphasizes that panels of approximately 6 somatic-specific antigens appropriate for each exposure type should be selected 3.
Critical Caveats
A positive serum IgG result does NOT confirm HP diagnosis - it only indicates exposure and sensitization 1. The test characteristics are suboptimal (sensitivity 83%, specificity 68% for distinguishing HP from other ILDs), making this insufficient as a standalone diagnostic test 1.
A negative result does NOT exclude HP - if clinical suspicion remains high despite negative serology, consider:
- Microbial analysis of the patient's specific environmental samples
- Production of "à la carte" antigens from microorganisms isolated from the patient's environment
- Specific inhalation challenge testing in controlled settings 3
Integration into Diagnostic Algorithm
Serum IgG testing should be used as one component of a multimodal diagnostic approach, not in isolation. The 2020 guideline recommends combining:
- Detailed exposure history (most critical first step)
- High-resolution CT findings
- Bronchoalveolar lavage with lymphocyte analysis (recommended for nonfibrotic HP, suggested for fibrotic HP)
- Serum IgG testing
- Histopathology when needed 1
The serum testing provides supportive data to increase diagnostic confidence but cannot confirm or exclude HP on its own 1. In Japan, bird-specific IgG (pigeons, budgerigars) and Trichosporon asahii antibody testing are covered by medical insurance, reflecting their clinical utility in appropriate contexts 2.
Practical Ordering Strategy
- Take detailed exposure history first - identify potential culprit antigens before ordering tests
- Select 6-8 specific antigens based on identified exposures rather than ordering broad panels
- Request ELISA methodology specifically (not precipitins)
- Include recombinant antigens when available for farmer's lung, metalworking fluid HP, and bird fancier's lung 3
- Consider environmental sampling if initial serology is negative but suspicion remains high
The most recent German (2025) and Australian/New Zealand (2024) guidelines continue to support this targeted approach to serologic testing as part of comprehensive HP evaluation 4, 5.