Why might a clinician order a diffusing capacity test?

A clinician may order a diffusing capacity test to determine if there are issues with the diffusion process across the alveolar-capillary membrane. This test specifically measures how well gases, such as oxygen and carbon dioxide, are exchanged between the air in the alveoli and the blood in the capillaries. Abnormal results can indicate a variety of conditions that affect the alveolar-capillary membrane, such as pulmonary fibrosis or emphysema, where the surface area for diffusion is compromised or the membrane itself becomes thickened or damaged.

This makes the assessment of diffusion capacity vital for diagnosing and managing diseases that impair gas exchange, leading to potential hypoxemia and respiratory distress. Other tests, such as spirometry, focus on airflow and lung volumes, while the diffusing capacity test specifically isolates the function of gas transfer in the lungs, thereby making it a crucial tool in the evaluation of pulmonary function.