A lung diffusion test (DLCO) measures how well oxygen moves from the alveoli into the blood. During the test you inhale a tiny amount of carbon monoxide, hold your breath briefly, then exhale; the exhaled gas is analyzed. Reduced diffusion can indicate emphysema, pulmonary fibrosis, pulmonary vascular disease, or anemia. It’s quick, noninvasive, and helps assess gas-exchange function.

Diffusion in the lungs is the passive movement of oxygen and carbon dioxide across the thin alveolar-capillary membrane. Oxygen moves from alveoli (high partial pressure) into pulmonary blood, while carbon dioxide moves from blood into alveoli to be exhaled. Efficient diffusion depends on membrane thickness, surface area, pressure gradients, and matching of ventilation and blood flow; disease or fluid can impair gas exchange.

A lung diffusion test (DLCO) is generally safe, noninvasive and brief. It involves breathing into a mouthpiece and exposure to a very small, harmless amount of carbon monoxide; adverse effects are rare. You may feel lightheaded, cough or briefly more breathless. It’s usually avoided in pregnancy and in certain conditions (recent heart attack, unstable angina, pneumothorax, recent eye/chest surgery). Discuss risks with your clinician.

Normal lung diffusion (DLCO) is generally considered 80–120% of the predicted value for age, sex, height and hemoglobin. Mild reduction is roughly 60–80% predicted, moderate 40–60% and severe <40%. Absolute DLCO values vary by lab; interpretation should account for hemoglobin, smoking and lung volume. Clinicians compare your DLCO with the appropriate predicted range.

Low lung diffusion often causes progressive shortness of breath, especially with exertion, decreased exercise tolerance and unexplained fatigue. Other signs include a persistent dry cough, rapid or shallow breathing, chest tightness and low oxygen levels causing dizziness, lightheadedness or bluish lips/fingertips. Symptoms may be subtle early on and worsen over time, warranting medical evaluation and lung function testing.

Pulmonary function tests vary widely by country and facility. Public systems may provide them free; in India private labs typically charge ₹300–₹2,000 (~$4–$25). In the US, simple spirometry often costs $50–$250, while full PFTs with lung volumes/DLCO range roughly $150–$1,000, depending on hospital vs outpatient setting and insurance coverage. Check with your provider or insurer for exact pricing.