Cytology of Bronchoalveolar Lavage (BAL) Fluid

Outline

Overview
Causes of Abnormal Cytology

BASICS

Overview

Material is collected from the small airways and alveoli by flushing with sterile saline, lactated Ringer's solution, or phosphate-buffered saline and suctioning back through an endoscope or cuffed BAL tube, which has been placed in a bronchus
Fluid is collected into sterile nonadherent tubes for cytology and bacterial culture. Samples should be kept on ice until analysis. If the analysis is delayed for more than a few hours, samples should be kept in EDTA tubes or in fixatives for cytology
Cytocentrifuged slides are preferred but sediment preparations and direct smears are adequate alternatives. Slides are preferable stained with automated Romanowsky, May–Grünwald–Giemsa, and toluidine blue stains to visualize mast cells
Total nucleated cells may be counted but this is not routine because standardizing the amount of saline recovered is difficult
Total protein of fluid is low and not routinely measured
BAL fluid from normal horses contains predominantly macrophages and lymphocytes, with small numbers of columnar epithelial cells, neutrophils, mast cells, and occasionally eosinophils. A differential cell count should be performed on 400 cells
Most samples contain a small amount of mucus
Presence of squamous epithelial cells indicates contamination from oropharynx

Pathophysiology

Material present in fluid from a BAL represents the region of lungs being sampled
Abnormalities include increased inflammatory cells, organisms, evidence of hemorrhage, increased mucus and goblet cells, and pollens/particulates that pass the mucociliary clearance apparatus
Chronic inflammation causes increased mucus
Neoplastic cells from lung tumors typically are not found in BAL samples
May not be diagnostic for focal lung lesions, mild diffuse disease, or severe, chronic airway disease that prevents lavage fluid from reaching affected alveoli

Causes of Abnormal Cytology

Acute or chronic inflammation
Equine asthma (IAD, heaves)
EIPH
Parasitic inflammation
Idiopathic eosinophilic inflammation
Neoplasia
EMPF

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
Laboratory Tests

DIAGNOSIS

Differential Diagnosis

Acute or Chronic Inflammation

Acute pulmonary inflammation is associated with increased neutrophils, which may be degenerative, especially when bacteria are present (e.g. pneumonia, pleuropneumonia)
If bacteria are primarily extracellular, examine samples for oropharyngeal contamination
Fungal elements are usually associated with increased macrophage and neutrophil numbers. They reflect their presence in the environment and a decrease in mucociliary clearance. It does not allow for a diagnosis of fungal pneumonia
Pneumocystis jiroveci (previously carinii) may be observed in immunosuppressed horses and more easily identified using Gömöri methenamine silver stains and other silver stains

Mild to Moderate Equine Asthma (IAD)

Characterized by increased neutrophils (>5–10%), mast cells (>2%), or eosinophils (>1%). Increases in one or more granulocyte populations may be present. Normal values may vary depending on the technique used for BAL fluid collection.

Severe Equine Asthma (Recurrent Airway Obstruction, Heaves)

BAL samples contain an increased percentage of neutrophils (usually >20–25%) with an increased amount of mucus or goblet cells
Eosinophil and mast cell numbers are rarely increased

EIPH

A few RBCs may be seen if mild trauma occurs during sampling
Phagocytized RBCs or macrophages containing breakdown products of hemoglobin suggest pulmonary hemorrhage before sampling. These may be present for 3 weeks following intrapulmonary bleeding

Parasitic Inflammation

Infection with the lungworm Dictyocaulus arnfieldi is associated with large numbers of eosinophils and macrophages; larvae are not usually seen.

Idiopathic Eosinophilic Pneumonia

Increased numbers of eosinophils are usually present.

Neoplasia

BAL fluid analysis is not typically useful in the diagnosis of pulmonary neoplasia.

Laboratory Tests

Bacterial or fungal cultures of BAL fluid are usually not recommended because of contamination of the upper airways during sampling
Baermann funnel fecal examination (lungworms)
PCR of BAL for equine herpesvirus 5 (EMPF)

Treatment ⬆ ⬇

TREATMENT