Bronchoalveolar Lavage Analysis

Bronchoalveolar lavage (BAL) samples cells and organisms from the distal airways and alveoli.

During flexible bronchoscopy, the tip is wedged in a segmental bronchus and 100 to 300 mL of sterile saline is instilled in aliquots and gently aspirated, recovering 30 to 60% of the fluid. The fluid is sent for microbiology, cell count and differential, cytology, and special studies.

Lavage is most useful in immunosuppressed patients with pulmonary infiltrates, in interstitial lung disease, in diffuse alveolar haemorrhage, and in ventilated patients with suspected pneumonia.

The test provides pathogens that sputum cannot (Pneumocystis, fungi, mycobacteria, viruses), and a cell pattern that narrows the differential of interstitial lung disease. It carries a low risk, with transient fever, cough and fall in oxygenation in a small proportion of patients, and bleeding or pneumothorax if biopsy is added.

Interstitial lung diseases comprise over 200 conditions with an incidence of 10 to 30 per 100 000 people a year, and idiopathic pulmonary fibrosis is the commonest. Pneumonia in immunosuppressed patients (HIV, transplant, haematological malignancy, biologics) has many possible causes, and a diagnosis from BAL is reached in 40 to 60%.

Indications. Immunosuppressed patients with new infiltrates, suspected opportunistic infection (Pneumocystis jirovecii, cytomegalovirus, Aspergillus, mycobacteria), diffuse interstitial lung disease of unclear cause (sarcoidosis, hypersensitivity pneumonitis, eosinophilic pneumonia, organising pneumonia, alveolar proteinosis), suspected diffuse alveolar haemorrhage, ventilator associated pneumonia not responding to treatment, suspected lymphangitic or lepidic malignancy, and non-resolving pneumonia.

Specimen. The first aliquot (bronchial wash) is kept apart from the later aliquots (alveolar).

Pooled alveolar return of at least 20 to 30 mL, in a non-wetting (polypropylene or siliconised) container on ice, is delivered to the laboratory within 1 hour.

Aliquots are used for:

• Gram stain and bacterial culture
• AFB smear, culture and Xpert
• fungal stains and culture
• Pneumocystis immunofluorescence or PCR
• viral PCR panel
• galactomannan
• cytology
• total and differential cell count (with fluid viability)
• flow cytometry

Use no more than 1% lidocaine since it is antimicrobial.

Normal cell differential (non-smoker). Total cells 100 to 200 per microL (higher in smokers, 400 to 600 per microL).

• Alveolar macrophages: 80 to 95% (higher in smokers).
• Lymphocytes: under 15% (CD4 to CD8 ratio about 1.5 to 3.5).
• Neutrophils: under 3%.
• Eosinophils: under 1%.
• Mast cells and plasma cells: under 0.5%.

Patterns.

Microbiology.

• Quantitative culture: over 10^4 cfu/mL supports bacterial pneumonia, and over 5% of cells with intracellular bacteria also supports it.
• Pneumocystis jirovecii: PCR is very sensitive (over 95%) but cannot separate colonisation from disease, whereas immunofluorescence is specific. Beta-D-glucan in serum and lavage supports it.
• Aspergillus: galactomannan in BAL with an index over 1.0 has sensitivity of 85 to 90% and specificity of 90 to 95% for invasive aspergillosis.
• Cytomegalovirus: viral inclusions (owl's eye cells) and immunostaining in lung tissue are needed to prove pneumonitis, and a positive PCR alone may reflect shedding.
• Tuberculosis: Xpert on BAL has sensitivity of about 80 to 90% in smear positive and 60 to 70% in smear negative disease.
• Respiratory viral PCR and Legionella PCR from lavage increase yield over sputum.

Critical values and findings needing immediate action.

• Pneumocystis found in an HIV or transplant patient with hypoxia: high dose co-trimoxazole and corticosteroids.
• Progressively bloody aliquots with haemosiderin laden macrophages: diffuse alveolar haemorrhage, requiring vasculitis workup, steroids and often immunosuppression.
• Positive AFB or Xpert: isolation and antituberculous treatment.
• Positive galactomannan or Aspergillus on culture in a neutropenic patient: antifungal treatment at once.
• Milky return in alveolar proteinosis: whole lung lavage is therapeutic.
• Malignant cells: oncology referral.

Interferences and pitfalls.

• Recovery under 30% or wrong site (a non-affected lobe) reduces diagnostic value. Lavage the most affected segment on CT.
• Contamination by upper airway flora can mislead cultures, and quantitative cultures and samples that avoid the working channel help.
• Cell counts are affected by smoking, age and processing delay, and by the lavage volume.
• Cell differential has a limited ability to diagnose idiopathic pulmonary fibrosis, and a multidisciplinary review of imaging and clinical data decides.
• Colonisation with Pneumocystis, cytomegalovirus, Candida and herpes simplex is common in immunosuppressed patients, and positive results must be matched with the clinical picture.
• Prior antibiotics lower the yield of bacterial culture.
• Bronchoscopy is dangerous in severe hypoxia or unstable patients, uncorrected bleeding disorders, and uncontrolled arrhythmia or unstable cardiac disease.
• Transbronchial or cryobiopsy increases diagnostic yield but also risk of pneumothorax and bleeding.

Special groups.

• Children: BAL is used for interstitial disease, infection in immunocompromised patients, and chronic aspiration (lipid laden macrophages), with volumes by weight.
• Ventilated patients: non-bronchoscopic mini-BAL gives similar information.
• HIV and transplant recipients: a combined panel is required for opportunistic infections.
• Older adults: neutrophilia and lymphocytosis increase modestly with age.
• Regions: availability of bronchoscopy is limited, and induced sputum is used for tuberculosis and Pneumocystis where BAL cannot be done.

Follow up tests. High resolution CT of the chest, lung function with diffusing capacity, serum ACE, calcium and immunoglobulins, hypersensitivity pneumonitis precipitins, autoantibodies and ANCA, anti-GBM antibodies, serum galactomannan and beta-D-glucan, cytomegalovirus viral load, HIV test, transbronchial or surgical lung biopsy, endobronchial ultrasound with lymph node sampling for sarcoidosis, and flow cytometry for lymphoma.