diffusion capacity of carbon monoxide (DLCO)

Principle

• used in the assessment of pulmonary function, alveolar integrity.
• dependent upon the thickness of the alveolo-capillary membrane, the hemoglobin level & the pulmonary capillary volume

Clinical significance

• measures ability of the lungs to transfer gas (CO2 & O2) across the alveolar-capillary membrane

Increases

• asthma (some) (FEV1/FVC < 0.7)
• pulmonary hemorrhage
• early CHF
• supine position
• after exercise
• polycythemia
• obesity
• left to right shunt

Decreases

• COPD. emphysema, bronchiectais (FEV1/FVC < 0.7)
• restrictive lung disease
• diffuse parenchymal lung disease (reduced lung volumes)
• pulmonary vascular disease, anemia (normal lung volumes)
  • isolated decrease in DLCO with otherwise normal PFTs
    • anemia - 1 g/dL decrease in hemoglobin decreases DLCO by 7%
    • pulmonary hypertension
    • recurrent pulmonary emboli
• pneumonectomy

Interpretation

Table

DLCO (% predicted)	Assessment
> 140%	increased
80-140%	normal
60-80%	mildly reduced
40-60%	moderately reduced
< 40%	severely reduced

• low lung volumes & normal DLCO suggests extrapulmonary etiology (obesity)

More general terms

• pulmonary function test (PFT)
• diffusion