Diagnostic Approach to Low Diffusion on Pulmonary Function Tests

Initial Diagnostic Workup

The American Thoracic Society recommends high-resolution CT (HRCT) chest as the primary imaging tool to detect ILD patterns, emphysema, pulmonary vascular abnormalities, and extent of disease 1, 2, 3
Complete spirometry with lung volumes by body plethysmography is necessary to identify obstructive, restrictive, or mixed patterns that may coexist with low DLCO 5
Arterial blood gases and pulse oximetry at rest and with exertion are essential to assess for hypoxemia 5, 2, 6
Transthoracic echocardiography is used to evaluate for pulmonary hypertension, right ventricular dysfunction, left heart disease, and valvular abnormalities 2, 3, 6

The European Respiratory Society states that DLCO reduction is the earliest and most sensitive PFT abnormality in ILD, often preceding changes in lung volumes 1, 5
Serial PFTs every 3-6 months for at least 1 year are required to establish disease trajectory and determine need for treatment 5
Bronchoalveolar lavage and lung biopsy are reserved for cases where diagnosis is inconclusive, infection is suspected, or neoplastic/lymphoproliferative disorders need exclusion 1, 5

The American College of Chest Physicians recommends pulmonary rehabilitation for symptomatic patients with ILD and impaired pulmonary function 5
Long-term oxygen therapy is indicated for resting oxygen saturation <88% or PaO2 <55 mmHg (or <60 mmHg with complications of chronic hypoxemia) 5
Vaccination against influenza and pneumococcal infection (Prevnar and Pneumovax) per CDC guidelines is mandatory 5
Smoking cessation counseling and intervention is essential, as smoking exacerbates both emphysema and ILD progression 1
PAH-specific therapy should only be initiated after right heart catheterization confirmation of pulmonary arterial hypertension 2, 3, 7