DLCO Testing Indications and Interpretations

Primary Diagnostic Indications

The European Respiratory Society recommends DLCO testing when evaluating patients with unexplained dyspnea, suspected interstitial lung disease, pulmonary vascular disease, emphysema, or when spirometry and lung volumes alone cannot explain the clinical picture 1, 2
When spirometry and lung volumes are normal but dyspnea persists, DLCO can identify early parenchymal disease, pulmonary vascular disorders, early interstitial lung disease (ILD), or early emphysema, as suggested by the European Respiratory Society 1, 2, 3
More than 40% of patients with normal FEV1 (>80% predicted) may have reduced DLCO (<80% predicted), making this test critical when spirometry appears reassuring but symptoms persist, according to Praxis Medical Insights 3

In the presence of restriction, a normal DLCO suggests chest wall or neuromuscular disorders, whereas a decreased DLCO indicates interstitial lung diseases, as indicated by the European Respiratory Society 1, 2, 4
Patients with ILD, sarcoidosis, and pulmonary fibrosis typically demonstrate low DLCO, as reported by the European Respiratory Society 1, 2

In the presence of airflow obstruction, a decreased DLCO strongly suggests emphysema rather than pure airway disease, according to the European Respiratory Society 1, 2, 4
Airway obstruction with low DLCO is also seen in lymphangioleiomyomatosis, as noted by the European Respiratory Society 1

Low DLCO is characteristic of chronic pulmonary embolism, primary pulmonary hypertension, and other pulmonary vascular diseases, with or without restriction of lung volumes, as indicated by the European Respiratory Society 1, 2, 4
Consider routine DLCO testing in all patients with severe and critical COVID-19 at 3 months from diagnosis, regardless of symptoms, as recommended by Clinical Microbiology and Infection 6
DLCO impairment has been found in up to 80% of patients at ICU discharge and 50-70% at 3-month follow-up after critical disease, according to Clinical Microbiology and Infection 6

High DLCO is associated with asthma, obesity, and intrapulmonary hemorrhage, which can provide diagnostic clues in the appropriate clinical context, as reported by the European Respiratory Society 1, 2, 4

Always adjust DLCO for hemoglobin levels, as anemia can cause falsely low DLCO values that do not reflect true gas exchange abnormalities, as recommended by the European Respiratory Society and Praxis Medical Insights 1, 2, 3, 4
Reduced DLCO is a predictor of cardiopulmonary complications and mortality even in patients with otherwise normal FEV1, emphasizing its importance in risk assessment, according to Praxis Medical Insights 3