Login or Register to unlock everything MedSchool has to offer!
Lung Function Tests
Lung Function Tests
Pulmonary function tests including spirometry, flow-volume loops, lung volumes and diffusion capacity can be used to diagnose and grade obstructive or restrictive lung disease.




  • Diffusing Capacity of Lung for Carbon Monoxide (DLCO) is a measure of the efficiency of lung gas transfer. This test is used to further characterise a respiratory defect following spirometry and lung volume testing, to provide evidence supporting a specific respiratory pathology.
    • Procedure

    • The patient inhales a mixture of helium (10%), carbon monoxide (0.3%), oxygen (21%) and nitrogen (68.7%), hold their breath for ten seconds and then exhale fully.
    • The levels of exhaled helium and carbon monoxide are used to calculate DLCO
    • The results may need to be corrected for the patient’s haemoglobin
    • Interpretation

    • Restrictive Pattern

    • Normal DLCO - chest wall or neuromuscular disorders
    • Low DLCO - interstitial lung disease
    • Obstructive Pattern

    • High DLCO - asthma
    • Normal DLCO - bronchiectasis, chronic bronchitis, α1-antitrypsin deficiency
    • Low DLCO - emphysema
    • Normal Spirometry

    • High DLCO - polycythaemia, pulmonary haemorrhage, left-to right intracardiac shunt
    • Low DLCO - anaemia, pulmonary hypertension, pulmonary embolus

Reduced DLCO

    • Causes of Reduced DLCO

    • Interstitial lung disease
    • Emphysema
    • Anaemia
    • Pulmonary hypertension
    • Pulmonary embolus

Elevated DLCO

    • Causes of Elevated DLCO

    • Asthma
    • Polycythaemia
    • Pulmonary haemorrhage
    • Left-to-right intracardiac shunt
Last updated on November 15th, 2017

Associated Diseases

Pulmonary Vascular Disease
Red Cell Disorders
Interstitial Lung Disease