Hypersensitivity Pneumonitis – Extrinsic Allergic Alveolitis

Lab Tests

Nonspecific testing

• CBC – neutrophilic leukocytosis most common abnormality
• C-reactive protein (CRP)

• Preferred test to detect inflammatory processes (Choosing Wisely: 20 Things Physicians and Patients Should Question, 2017; American Society for Clinical Pathology)logy)
• Frequently elevated
• If CRP not available, order erythrocyte sedimentation rate (ESR)

• IgE – usually normal

Serum precipitating antibodies – testing based on suspected exposure

• Positive findings are only suggestive and help document patient exposure to antigen
• Low titers do not exclude disease
• Enzyme-linked immunosorbent assay (ELISA) more sensitive than immunodiffusion

Other Tests

Pulmonary function studies

• Restrictive or mixed obstructive and restrictive patterns with decrease in diffusing capacity of lung for carbon monoxide (DLCO) usually <80% – normal results do not exclude disease
• No discriminatory power to differentiate HP from other interstitial lung diseases

Arterial blood gases

• demonstrate hypoxemia only with exercise in acute and subacute disease

Invasive testing – BAL using bronchoscopy

• Lymphocytosis

• Usual presentation is ≥30% in nonsmokers and ≥20% in smokers
• CD3+/CD8+/CD56+/CD57+/CD10-

• CD4+/CD8+

• Usually <1 in acute disease but may be >1 in chronic disease
• May help differentiate HP from sarcoidosis, where ratio is usually >1

• Eosinophilia common (75%) in advanced disease

Hypersensitivity Pneumonitis I

Method: Qualitative Immunodiffusion

Recommended Use

Evaluate patients suspected of having hypersensitivity pneumonitis induced by exposure to Aspergillus fumigatus,

Thermoactinomyces vulgaris, Aureobasidium pullulans, or Micropolyspora faeni

Hypersensitivity Pneumonitis 2

Method: Qualitative Immunodiffusion

Recommended Use

Evaluate patients suspected of having hypersensitivity pneumonitis induced by exposure to Aspergillus fumigatus,

Thermoactinomyces vulgaris, Aureobasidium pullulans, or Micropolyspora faeni

Hypersensitivity Pneumonitis Panel

Method: Qualitative Immunodiffusion

Recommended Use

Evaluate patients suspected of having hypersensitivity pneumonitis induced by exposure to Aspergillus fumigatus,

Thermoactinomyces vulgaris, Aurebasidium pullulans, Micropolyspora faeni, Aspergillus flavus, Saccharomonospora viridis, or Thermoactinomyces candidus

Lymphocyte Subset Panel 4 – T-Cell Subsets Percent and Ratio, Bronchoalveolar Lavage

Method: Flow Cytometry

Recommended Use

Support the diagnosis of sarcoidosis

Hypersensitivity Pneumonitis Extended Panel (Farmer’s Lung Panel)

Method: Qualitative Immunodiffusion/Quantitative ImmunoCAP Fluorescent Enzyme Immunoassay
Recommended Use

Panel includes allergen and antibody testing from hypersensitivity pneumonitis panels as well as allergen testing, Phoma betae, food, beef, pork, epidermals, and animal proteins and feathers