What blood investigations are used to diagnose hypersensitivity pneumonitis (HP)?

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Last updated: April 24, 2025 • View editorial policy

From the Guidelines

Blood investigations for hypersensitivity pneumonitis should include specific precipitating antibodies (IgG) against suspected antigens, complete blood count, C-reactive protein, and erythrocyte sedimentation rate. The most important test is the specific IgG antibody panel, which identifies antibodies against common antigens like farmer's lung antigens, bird proteins, fungi, and chemical compounds. These tests should be ordered when clinical symptoms and imaging suggest hypersensitivity pneumonitis, as recommended by the American Thoracic Society 1. A complete blood count may show leukocytosis with neutrophilia in acute phases, while inflammatory markers like CRP and ESR are often elevated. Serum total IgE levels may be normal or slightly elevated but are less specific than precipitating IgG antibodies. Pulmonary function tests and bronchoalveolar lavage complement these blood tests by demonstrating restrictive patterns and lymphocytosis, respectively. It's essential to note that positive serology only indicates exposure to an antigen, not necessarily disease, so results must be interpreted alongside clinical findings and exposure history, as emphasized in the guideline 2. Testing should be performed before starting corticosteroid treatment, as this may suppress antibody production and lead to false-negative results. The sensitivity and specificity of serum IgG testing against potential antigens associated with HP are 83% and 68%, respectively, as reported in a study published in the American Journal of Respiratory and Critical Care Medicine 1. Key points to consider when ordering blood investigations for hypersensitivity pneumonitis include:

  • Specific IgG antibody panel to identify antibodies against common antigens
  • Complete blood count to show leukocytosis with neutrophilia in acute phases
  • Inflammatory markers like CRP and ESR to assess disease activity
  • Pulmonary function tests and bronchoalveolar lavage to demonstrate restrictive patterns and lymphocytosis
  • Interpretation of results alongside clinical findings and exposure history, as recommended by the guideline 3.

From the Research

Blood Investigations for Hypersensitivity Pneumonitis

  • Blood investigations for hypersensitivity pneumonitis (HP) may include serum IgG testing for the presence of antigen exposure, as mentioned in the study 4
  • These tests can help increase diagnostic confidence, especially when combined with other diagnostic criteria such as exposure identification, HRCT findings, and lung biopsy results 4
  • The role of adjunctive tests, including serum IgG testing, is discussed in the context of supporting diagnostic confidence for HP diagnosis 5
  • Bronchoalveolar lavage lymphocytosis is also an important test in the diagnosis of HP, as it can help identify patients with fibrotic and progressive disease 6
  • Pulmonary function testing may also be used as an adjunctive test to support the diagnosis of HP 5

Diagnostic Criteria

  • The diagnosis of HP requires a thorough exposure history, multidisciplinary discussion of clinical and radiologic data, and assessment of bronchoalveolar lavage lymphocytosis and histopathologic findings 6
  • Radiographic and histopathologic diagnostic criteria are presented in the study 5, including new guideline recommendations
  • The study 4 also discusses the diagnostic criteria for HP, including HRCT findings of ground-glass opacities, centrilobular nodules, and mosaic attenuation, with traction bronchiectasis and honeycombing in fibrotic cases

Classification and Treatment

  • Patients with HP may be categorized as having non-fibrotic or fibrotic HP, with the presence of fibrosis associated with worse outcomes 6
  • The treatment of HP includes avoidance of the implicated exposure, immunosuppression, and anti-fibrotic therapy in select cases, as discussed in the study 4

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Hypersensitivity Pneumonitis: An Updated Diagnostic Guide for Internists.

The Medical clinics of North America, 2022

Research

Diagnosis, course and management of hypersensitivity pneumonitis.

European respiratory review : an official journal of the European Respiratory Society, 2022

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.