Overview
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
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