Bronchoalveolar lavage (BAL) is a medical procedure used to collect fluid from the small airways and air sacs (alveoli) deep within the lungs. The term “lavage” refers to washing or rinsing these structures. This minimally invasive diagnostic tool provides a direct, cellular-level view into the lower respiratory tract, which is otherwise difficult to access. By washing a small segment of the lung, practitioners retrieve cells and non-cellular components from the alveolar surface, offering insights into underlying lung pathology.
The Bronchoalveolar Lavage Procedure
The procedure begins with a flexible bronchoscope, a thin, lighted tube with a camera, inserted through the nose or mouth and guided into the airways. The scope’s flexibility allows the physician to navigate the branching air passages to reach a specific lung subsegment, often guided by imaging. Once the bronchoscope is wedged into a smaller airway, the washing process begins.
Sterile saline solution, typically 50 to 60 milliliters per aliquot, is instilled through a channel in the bronchoscope into the targeted lung area. This saline washes the surface of the small airways and alveoli, mixing with cells and fluids in the epithelial lining. After a brief dwell time, the fluid is gently aspirated back through the bronchoscope’s channel into a collection trap.
Aspiration must be performed with controlled, gentle suction to prevent the airway from collapsing and compromising fluid return. Only a fraction of the instilled volume, typically 40 to 60 percent, is recovered. This retrieved fluid contains a concentrated sample of the lower respiratory tract’s cellular and soluble components and is immediately sent for laboratory analysis.
Clinical Conditions Diagnosed by BAL
Bronchoalveolar lavage is used for differential diagnosis across a range of pulmonary conditions, particularly those affecting the lung tissue (parenchyma). It frequently investigates unexplained radiographic pulmonary infiltrates or persistent hypoxemia when standard tests are inconclusive. The procedure helps identify opportunistic and atypical respiratory infections, especially in immunocompromised patients.
BAL fluid can be tested for pathogens such as Pneumocystis jirovecii pneumonia, mycobacteria, fungi, or viruses, which are often difficult to detect otherwise. BAL is also a standard tool for interstitial lung diseases (ILDs), disorders characterized by scarring or inflammation of the lung tissue. Specific ILDs, including sarcoidosis, hypersensitivity pneumonitis, and chronic beryllium disease, often show characteristic cellular patterns in the retrieved fluid.
BAL is employed to diagnose conditions such as diffuse alveolar hemorrhage (bleeding into the air sacs) or pulmonary alveolar proteinosis (accumulation of abnormal protein material). The fluid can also be examined for suspected malignancies, including diffuse forms of lung cancer or metastatic disease. BAL findings often provide a definitive diagnosis, helping to avoid more invasive procedures like surgical lung biopsy.
Interpreting the Cellular and Biochemical Analysis
The diagnostic value of BAL lies in the detailed laboratory examination of the retrieved fluid for cellular composition and biochemical markers. Initial analysis determines the total cell count and the differential cell count, identifying the relative proportions of immune cells. In a healthy, non-smoking individual, the fluid is predominantly composed of alveolar macrophages, typically accounting for 80 to 90 percent of the cells.
Shifts in the differential count provide clues about the type of inflammation occurring in the lung. For instance, a significantly increased percentage of lymphocytes, often exceeding 25 percent, suggests granulomatous diseases such as sarcoidosis or hypersensitivity pneumonitis. If the lymphocyte count is high, further subtyping, specifically looking at the ratio of CD4+ to CD8+ T-lymphocytes, can help distinguish between these two conditions.
An elevated neutrophil count, particularly above three percent, may suggest inflammatory processes such as acute lung injury, aspiration pneumonia, or idiopathic pulmonary fibrosis. Conversely, a high number of eosinophils is a distinct finding. An eosinophil percentage greater than 25 percent is suggestive of acute or chronic eosinophilic pneumonia.
The fluid is also subjected to specific diagnostic tests beyond the cellular analysis:
- Microbiological studies are performed, including cultures, stains, and PCR tests, to identify bacteria, viruses, fungi, or mycobacteria.
- Cytology is performed to search for malignant cells, which can confirm a diagnosis of lung cancer or leukemia.
- Biochemical markers, such as protein levels, can be measured.
- The presence of hemosiderin-laden macrophages can diagnose conditions like alveolar proteinosis or diffuse alveolar hemorrhage.
Patient Preparation, Risks, and Post-Procedure Care
Proper patient preparation ensures the safety and success of the BAL procedure. Patients must fast for approximately six hours before the procedure to minimize the risk of aspirating stomach contents. The procedure is typically performed under conscious sedation to help the patient relax, and the throat is numbed with a topical anesthetic.
While BAL carries low-frequency risks, it is generally well-tolerated. The most common side effects include a temporary drop in blood oxygen levels (hypoxemia), a slight cough, and shortness of breath (dyspnea), which usually resolve quickly. A low-grade fever within the first 24 hours is observed in up to 20 percent of patients.
More serious complications, such as significant bleeding or a collapsed lung (pneumothorax), are rare and are usually associated with additional procedures, like biopsies, performed at the same time. After the procedure, patients are monitored until sedative effects wear off and vital signs stabilize. Once the numbing agent wears off and the gag reflex returns, the patient can typically resume eating and drinking and return home the same day.