MedSchool: Ace Your OSCEsThe Medical Company
GET - On the App Store
Lung Function Tests


February 15th, 2021


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
Next Page
Want more info like this?
  • Your electronic clinical medicine handbook
  • Guides to help pass your exams
  • Tools every medical student needs
  • Quick diagrams to have the answers, fast
  • Quizzes to test your knowledge
Sign Up Now

Snapshot: Initialising...