Bronchoalveolar Lavage (BAL)

I. Introduction & Definition

Definition: A diagnostic procedure performed during flexible bronchoscopy where saline is instilled into a subsegment of the lung and aspirated back to sample the alveolar and distal airway milieu.
Concept: Often referred to as a "Liquid Biopsy" of the lower respiratory tract.
Site: usually performed in the Right Middle Lobe (RML) or Lingula (highest yield due to anatomy), or the most affected area radiologically.

II. Indications

1. Diagnostic Indications

Non-resolving Pneumonia: To identify resistant bacteria, fungi (Aspergillus), or Pneumocystis jirovecii (PCP).
Immunocompromised Host: Evaluation of opportunistic infections.
Interstitial Lung Disease (ILD): To determine cellularity (lymphocytic vs. neutrophilic) or identify hemorrhage.
Aspiration Syndromes: Detection of lipid-laden macrophages.
Pulmonary Hemorrhage: Diagnosis of Diffuse Alveolar Hemorrhage (DAH).

2. Therapeutic Indications

Pulmonary Alveolar Proteinosis (PAP): Whole lung lavage to wash out surfactant protein accumulation.
Mucus Plugging: To dislodge tenacious plugs (e.g., in severe Asthma or Cystic Fibrosis).

III. Procedure (Technique)

Wedging: The bronchoscope tip is wedged into a segmental or subsegmental bronchus.
Instillation: Sterile non-bacteriostatic saline is instilled.
- Dose: 1 ml/kg per aliquot (usually 3 aliquots).
Aspiration: Gentle suction is applied to retrieve the fluid (effluent).
- Adequacy: >40% recovery of instilled volume is considered adequate.

IV. Analysis and Interpretation

The fluid is sent for Microscopy, Culture, Cytology, and PCR.

1. Normal Pediatric BAL Profile

Macrophages: 80–90% (Predominant cell type).
Lymphocytes: <10%.
Neutrophils: <3%.
Eosinophils: <1%.

2. Abnormal Patterns

Finding	Differential Diagnosis
Neutrophilia (>50%)	Bacterial pneumonia, Aspiration, Cystic Fibrosis.
Lymphocytosis (>15%)	Hypersensitivity Pneumonitis, Sarcoidosis, Viral infection, TB.
Eosinophilia (>5%)	Asthma, ABPA, Parasitic infection, Drug reaction.
Hemosiderin-laden Macrophages	Diffuse Alveolar Hemorrhage (DAH), Idiopathic Pulmonary Hemosiderosis.
Lipid-laden Macrophages	Chronic Aspiration (sensitive but non-specific).
Milky/Opaque Fluid	Pulmonary Alveolar Proteinosis (PAP).
Silver Stain (+)	Pneumocystis jirovecii Pneumonia (PCP).

V. Complications

Transient Fever: Most common (10–30% of cases) due to cytokine release.
Hypoxemia: Transient drop in SpO2 during and immediately after the procedure.
Bronchospasm.
Bleeding: Usually minor/self-limiting.