What does BAL (Bronchoalveolar Lavage) stand for in the context of a patient with suspected hypersensitivity pneumonitis (HP)?

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Last updated: January 7, 2026 • View editorial policy

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What BAL Stands For

BAL stands for Bronchoalveolar Lavage, a diagnostic procedure used to sample cells and fluid from the lower respiratory tract, particularly valuable in evaluating interstitial lung diseases including hypersensitivity pneumonitis. 1

Definition and Purpose

  • BAL is a bronchoscopic procedure where sterile saline is instilled into a subsegment of the lung (typically the middle lobe) and then aspirated to retrieve cells and fluid from the alveolar spaces for cellular and biochemical analysis. 1

  • The procedure provides direct sampling of the alveolar compartment, allowing analysis of inflammatory cells, infectious organisms, and other diagnostic markers that can help distinguish between different types of interstitial lung disease. 1

Clinical Application in Hypersensitivity Pneumonitis

Diagnostic Value

  • For nonfibrotic HP, the American Thoracic Society recommends obtaining BAL fluid for lymphocyte cellular analysis as a key diagnostic step, with lymphocytosis ≥30% supporting the diagnosis. 1

  • For fibrotic HP, the American Thoracic Society suggests BAL with lymphocyte cellular analysis, though with slightly less strength of recommendation compared to nonfibrotic disease. 1

  • BAL lymphocytosis >50% is highly suggestive of hypersensitivity pneumonitis or cellular nonspecific interstitial pneumonia, helping differentiate HP from other interstitial lung diseases. 1

Diagnostic Thresholds

  • A lymphocyte differential count >25% suggests granulomatous disease including HP, sarcoidosis, or chronic beryllium disease. 1

  • The percentage of BAL fluid lymphocytes is significantly higher in both fibrotic and nonfibrotic HP compared to idiopathic pulmonary fibrosis, with a threshold of 20% distinguishing fibrotic HP from IPF with 69% sensitivity and 61% specificity. 2

  • The most important application of BAL is to increase the index of suspicion for alternative disorders in patients with suspected IPF, including hypersensitivity pneumonitis, by demonstrating lymphocytosis >30%. 1

Procedural Considerations

  • BAL should be performed when patients are in active antigen exposure, as this significantly improves diagnostic yield compared to when patients are out of exposure. 3

  • The procedure involves instilling 3 mL/kg body weight of normal saline warmed to body temperature via flexible bronchoscopy, typically in the middle lobe. 4

  • In addition to lymphocytosis, BAL in HP may show increased mast cells (>1%), neutrophils (>3%), and lymphocytes (>50%), which is suggestive of acute hypersensitivity pneumonitis. 1

Integration into Diagnostic Algorithm

  • The American Thoracic Society diagnostic algorithm for HP includes HRCT scan and BAL fluid lymphocyte cellular analysis as initial diagnostic steps, followed by multidisciplinary discussion. 1, 5

  • High diagnostic confidence can be achieved when all three elements are present: documented exposure to an inciting agent, characteristic HRCT findings, and BAL lymphocytosis ≥30%. 5

  • BAL has additional value in nonfibrotic HP for identifying or excluding pulmonary infection, especially Mycobacterium tuberculosis in endemic areas. 1

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

5
Guideline

Diagnostic Criteria for Hypersensitivity Pneumonitis

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2025

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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.

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